A kidney stone exits your body by traveling through the same plumbing that carries urine: from the kidney into the ureter (the narrow tube connecting each kidney to the bladder), then into the bladder, and finally out through the urethra when you urinate. The journey through the ureter is where nearly all the pain and drama happen, because the ureter is only a few millimeters wide and the stone has to be squeezed along by muscular contractions. The whole process can take anywhere from a few days to several weeks, depending mostly on the stone’s size and where it starts.
The Route From Kidney to Toilet
Think of the path as four stages, each with a different feel and different level of difficulty for the stone.
- Kidney to ureter: The stone forms inside the kidney, often sitting there painlessly for weeks or months. Pain typically begins when the stone drops into the ureter, the narrow tube about 25 to 30 centimeters long that funnels urine downward to the bladder.
- Upper ureter: The first stretch of the ureter is where many stones lodge early on. You may feel deep flank pain on the affected side, sometimes radiating toward the back.
- Mid and lower ureter: As the stone moves down, pain often shifts toward the lower abdomen and groin. Some people notice an increasing urge to urinate as the stone approaches the bladder.
- Bladder and urethra: Once the stone drops into the bladder, the worst pain usually ends. The urethra is wider than the ureter, so passing the stone during urination is often anticlimactic. You may feel a brief sting or pressure, and then it’s out.
The transition from the ureter into the bladder is the final bottleneck. After that, the stone essentially rides out with your urine stream. Many people report that the moment of actually urinating the stone out is far less painful than the days spent waiting for it to reach the bladder.
What Actually Pushes the Stone Along
Your ureters are not passive pipes. They are muscular tubes that contract in rhythmic waves called peristalsis, the same kind of squeezing motion your intestines use to move food. These waves push urine from the kidney to the bladder, and they push a stone the same way, though a stone moves much more slowly and with much more resistance.
The ureter wall is elastic and stretchy, which helps it accommodate a stone somewhat larger than its resting diameter. Compression waves behind the stone build up pressure and nudge it forward a little at a time. When the stone is too large or gets wedged at a narrow point, those same contractions generate intense, cramping pain because the muscle is squeezing hard against an object that won’t budge. Urine backs up behind the obstruction, which can cause the kidney to swell, a condition called hydronephrosis. That backup pressure also contributes to the deep, aching flank pain many people describe as among the worst they’ve ever felt.
Where Stones Get Stuck
The ureter is not uniformly narrow. There are specific anatomical chokepoints where stones are most likely to lodge. Traditionally, textbooks describe three: the junction where the kidney meets the ureter (the ureteropelvic junction), the spot where the ureter crosses over the large blood vessels near the pelvis, and the point where the ureter tunnels through the bladder wall (the ureterovesical junction). In practice, the evidence is a bit more nuanced.
A review of stone locations in patients referred for treatment found two clear peaks in where stones cluster: the upper ureter near the kidney and the very lowest segment where the ureter enters the bladder. The supposed middle chokepoint, where the ureter crosses the pelvic blood vessels, did not show up as a distinct peak in that data.
1PubMed. Stones lodge at three sites of anatomic narrowing in the ureter: clinical fact or fiction?A separate imaging study found that the peak site of stone lodging in the upper ureter may actually be slightly lower than the ureteropelvic junction itself, at a newly identified area of narrowing called the crossing point.
2Urology. The Peak Site of Stone Distribution in the Upper Ureter is Unlikely the Ureteropelvic JunctionWhat this means for you is straightforward: the top and bottom of the ureter are where a stone is most likely to stall. A stone stuck near the kidney tends to cause flank and back pain; a stone stuck near the bladder tends to cause lower abdominal and groin discomfort, sometimes with urgency and burning during urination.
How Pain Shifts as the Stone Moves
One of the distinctive features of kidney stone pain is that it migrates. Because the stone is physically moving through the ureter over hours or days, where you feel pain changes along with it. A stone high in the ureter typically causes sharp, crampy pain in the flank, the area between your ribs and hip on one side. As it descends, the pain often wraps around toward the front of the abdomen and eventually down toward the groin. Men sometimes feel it in the testicle; women may feel it radiating toward the labia. This happens because the nerves serving the ureter overlap with nerves serving those areas, creating referred pain.
The pain tends to come in waves rather than staying constant, matching the peristaltic contractions of the ureter. You might have 20 to 60 minutes of severe cramping followed by a lull, then another wave. Nausea and vomiting are common during the peaks. Blood in the urine, sometimes visible and sometimes only detectable on a test strip, is typical because the stone scrapes the ureter lining as it moves.
Size and Location Determine Whether You’ll Pass It
The single biggest factor in whether a stone will pass on its own is its width. Stones are measured in millimeters, and every millimeter matters.
A large study tracking nearly 400 ureteral stones over 20 weeks found dramatic differences in spontaneous passage rates by size: stones up to 3 mm passed about 98% of the time, 4 mm stones passed roughly 81% of the time, 5 mm stones about 65%, and 6 mm stones only about a third of the time. Once stones reached 6.5 mm or larger, the spontaneous passage rate dropped to around 9%.
3PubMed Central. Size matters: The width and location of a ureteral stone accurately predict the chance of spontaneous passageTime matters too. In an earlier study of 75 patients, the average time to passage was about 8 days for stones 2 mm or smaller, about 12 days for stones between 2 and 4 mm, and about 22 days for stones 4 mm or larger. For 95% of stones to pass, the timeline stretched to roughly 31 to 40 days depending on size. Stones that were smaller, located further down the ureter, and on the right side were more likely to pass on their own.
4PubMed. Time to stone passage for observed ureteral calculi: a guide for patient educationLocation matters independently of size. A 5 mm stone already near the bladder has a much better chance of passing than the same 5 mm stone lodged near the kidney. This is one reason your doctor may recommend watchful waiting even if the stone sounds large, depending on where imaging shows it sitting.
Medications That Help Stones Pass
When a stone is in the “maybe it will pass” size range, roughly 4 to 10 mm, doctors sometimes prescribe a class of medications called alpha-blockers. The most commonly used one is tamsulosin, a drug originally developed for prostate problems that also relaxes the smooth muscle in the ureter wall. The idea is to widen the ureter slightly and reduce spasms, giving the stone an easier path.
A meta-analysis pooling 46 studies found that tamsulosin improved the overall stone expulsion rate compared to control treatment, roughly 81% versus 71%. It also shortened the time to expulsion by about 3.5 days on average. The benefit was most clear for larger stones (above 6 mm); for smaller stones under 6 mm, the expulsion rates were similar whether patients took tamsulosin or not.
5PubMed Central. Is tamsulosin effective for the passage of symptomatic ureteral stones A systematic review and meta-analysisA more recent meta-analysis of randomized placebo-controlled trials confirmed that tamsulosin significantly increased the stone expulsion rate and shortened the time to passage by about 3 days without increasing side effects.
6PubMed Central. Tamsulosin versus placebo for medical expulsive therapy in ureteral calculi: a systematic review and meta-analysis of randomized controlled trialsAlong with tamsulosin, you’ll typically be given pain medication (usually a nonsteroidal anti-inflammatory drug and sometimes a stronger painkiller) and told to drink plenty of fluids to keep urine flowing. The combination of pain control, muscle relaxation, and high fluid volume is called medical expulsive therapy. It is the standard first approach for stones that have a reasonable chance of passing.
When a Stone Won’t Pass on Its Own
If a stone is too large, has been stuck too long, or is causing complications like infection or worsening kidney function, doctors intervene to remove or break it up. The two main options for ureteral stones are shockwave lithotripsy and ureteroscopy.
Shockwave lithotripsy is the less invasive of the two. You lie on a table while a machine sends focused shockwaves through your skin to the stone’s location, guided by X-ray or ultrasound. The shockwaves break the stone into small fragments that you then pass naturally over the following days or weeks. It can be done as an outpatient procedure without general anesthesia, which is a significant practical advantage.
Ureteroscopy involves passing a thin, flexible scope through the urethra and bladder, up into the ureter, and directly to the stone. Once there, the stone can be broken with a laser and the fragments removed. This generally requires general anesthesia and is done as a day case. Ureteroscopy has a higher single-treatment success rate, meaning the stone is more likely to be completely cleared in one session. However, it requires more hospital time and carries a somewhat higher risk of complications than shockwave lithotripsy, which may need repeat sessions.
7PubMed Central. Shockwave lithotripsy compared with ureteroscopic stone treatment for adults with ureteric stones: the TISU non-inferiority RCTAfter either procedure, a temporary ureteral stent, a thin plastic tube placed inside the ureter, may be left in place for a few days to a few weeks to keep the ureter open and allow any remaining fragments and urine to drain freely.
8PubMed Central. Comprehensive overview of ureteral stents based on clinical aspects, material and designWarning Signs That Require Emergency Care
Most kidney stones, however painful, are not dangerous. But there is one scenario that turns a miserable experience into a genuine emergency: infection behind an obstructing stone. When a stone blocks urine flow and bacteria are present, the trapped, infected urine can rapidly progress to urosepsis, a life-threatening bloodstream infection. This is a urologic emergency requiring surgical decompression, meaning urgent placement of a stent or a drain through the skin into the kidney to relieve the obstruction and let the infected urine out.
9PubMed Central. A real pain in the back…or maybe not- a case series of urosepsis due to obstructing calculi identified on ultrasoundIn one study of patients with obstructing ureteral stones who arrived at the emergency department, about 17% developed sepsis. The strongest predictors were a body temperature at or above 38°C (100.4°F), being female, and elevated inflammatory markers on blood tests. Larger stones were also associated with higher sepsis risk.
10PubMed. Clinical and time-related predictors of sepsis in patients with obstructive uropathy due to ureteral stones in the emergency settingYou should seek emergency care if you have stone symptoms combined with fever or chills, inability to keep fluids down due to persistent vomiting, complete inability to urinate, or pain that is unresponsive to prescribed medication. Fever in the setting of a known or suspected stone should always be treated urgently.
Stones You Never Feel
Not every stone announces itself with agonizing pain. A small number of ureteral stones are discovered incidentally on imaging done for other reasons, with no symptoms at all. In one long-term review covering over 3,700 patients with ureteral stones, about 1.1% had completely asymptomatic stones. These silent stones were found scattered along the ureter, and their average size was surprisingly large, around 10 mm, which is well above the range that would normally be expected to pass on its own. The vast majority of these required treatment: shockwave lithotripsy in most cases, with a smaller number treated by ureteroscopy.
11PubMed. The silence of the stones: asymptomatic ureteral calculiEven stones sitting in the kidney, not yet in the ureter, can sometimes cause painless obstruction. A study tracking asymptomatic kidney stones found that about 3% caused silent obstruction requiring intervention after an average of about three years.
12PubMed. The natural history of nonobstructing asymptomatic renal stones managed with active surveillanceThe takeaway is that the absence of pain does not guarantee a stone is harmless. If you have a history of stones, follow-up imaging at intervals your doctor recommends is worthwhile even when you feel fine.
Kidney Stones During Pregnancy
Pregnancy complicates kidney stone management in several ways. Diagnosis is harder because the usual go-to imaging, CT scan, uses ionizing radiation that poses risks to the fetus. Ultrasound is the first-line imaging tool in pregnancy, but it is less sensitive for detecting small ureteral stones. Treatment options are more limited too: shockwave lithotripsy and percutaneous surgery are both contraindicated during pregnancy.
13Nature Reviews Urology. Kidney stones during pregnancyThe standard approach is conservative, meaning watchful waiting with pain management, just as in non-pregnant adults. However, the rate of spontaneous passage during pregnancy appears to be lower than in the general population. One study of 90 pregnant women with stones found that only about 48% passed the stone on their own; about 30% needed surgical intervention during the pregnancy, and another 25% required definitive surgery after delivery.
14PubMed. Diagnosis of urolithiasis and rate of spontaneous passage during pregnancyWhen conservative management fails and the stone must be addressed during pregnancy, ureteroscopy has emerged as a safe and effective option. If the situation involves an obstructing stone with infection, immediate drainage via a ureteral stent or a nephrostomy tube is essential, just as it would be in a non-pregnant patient, because urosepsis is dangerous for both the mother and fetus.
15PubMed Central. Renal stones in pregnancyHydration and Helping the Process Along
You will hear “drink lots of water” from every doctor, nurse, and well-meaning relative during a stone episode. The logic is simple: more fluid means more urine, and more urine means a stronger current to push the stone along. It also dilutes the minerals that formed the stone in the first place.
A systematic review spanning two decades of research confirmed that higher fluid intake is consistently associated with increased urine output and reduced stone formation. Water is the best default choice. Interestingly, the type of fluid matters for prevention: grapefruit, apple, and orange juices reduced the concentration of calcium oxalate (the most common stone ingredient) in urine, while cranberry juice increased it. Water with very high calcium content seemed to modestly increase calcium oxalate formation. For the purpose of actively passing a stone, though, the priority is volume, not type. Aim for enough fluid to produce at least two to three liters of urine per day, which for most people means drinking well beyond the point of comfortable thirst.
16PubMed Central. The role of fluid intake in the prevention of kidney stone disease: A systematic review over the last two decadesStaying physically active, as tolerated, may also help. Walking and gentle movement promote urinary flow and may help the stone work its way down, though the evidence for exercise specifically accelerating stone passage is thin. The bigger benefit of staying mobile is practical: it keeps you functional and out of bed, which makes the waiting period more bearable.
Catching the Stone and Why It Matters
Your doctor will likely give you a small mesh strainer and ask you to urinate through it until the stone passes. This is not busywork. Catching the stone and having it analyzed tells you what it’s made of, and that information directly shapes the plan to prevent future stones. Calcium oxalate, calcium phosphate, uric acid, struvite, and cystine stones all have different dietary and medical strategies to reduce recurrence.
Stone composition analysis is done using techniques like X-ray diffraction or infrared spectroscopy, which identify the mineral content precisely. In some cases, stone cultures are also performed to check for bacteria embedded within the stone itself, which can inform antibiotic decisions if infection was involved.
17PubMed Central. Does a kidney stone culture make sense? The findings of microbiological cultures of kidney stones and correlation with stone composition, preoperative urine testing and postoperative SIRSIf you pass a stone at home, drop it in a clean container (a small zip-lock bag works fine) and bring it to your next urology appointment. People who have had one stone have a roughly 50% chance of forming another within the next five to ten years, so the composition result is one of the most useful pieces of data your doctor can get for long-term prevention planning.
Kidney Stones in Children
Kidney stones are not exclusively an adult problem. Pediatric stone disease has become more commonly diagnosed in recent decades, and the passage dynamics differ from adults in some respects. Children’s ureters are smaller, but their stones also tend to be smaller. In one large pediatric series, about 46% of children passed their stones spontaneously, while about 28% needed shockwave lithotripsy, of whom about 71% became stone-free.
18PubMed Central. Pediatric stone disease: an evolving experienceThe management approach in children mirrors adults in principle: small stones get a trial of passage with pain control and hydration, while larger or complicated stones require intervention. The threshold for intervention may be lower in children because prolonged obstruction in a developing kidney is a concern, and children are less able to tolerate extended periods of pain. Parents should know that the same warning signs, fever with stone symptoms or inability to keep fluids down, apply to kids and warrant urgent evaluation.
How Stone Surgery Has Changed Over the Centuries
For most of recorded history, a kidney stone that would not pass on its own was a terrifying problem. The earliest surgical descriptions date to the Roman writer Celsus, who documented “perineal lithotomy,” essentially cutting into the perineum to extract a bladder stone without anesthesia. In 1561, Pierre Franco performed the first suprapubic lithotomy, cutting through the lower abdomen into the bladder. These operations were brutal, frequently fatal, and so dreaded that the Hippocratic Oath included a line about not cutting for stone, deferring instead to those who specialized in it.
19PubMed Central. The history of urinary stones: in parallel with civilizationThe modern era began in 1980 with the introduction of extracorporeal shockwave lithotripsy, which could break stones without any incision at all. That single innovation transformed urology and made stone treatment an outpatient affair for most people. Today, even stones that require direct intervention are handled through natural body openings using flexible scopes and lasers, with no external cuts. A person passing a kidney stone in the 21st century is dealing with one of the oldest medical problems in human history, but with options that would have been unimaginable even 50 years ago.