A man with one testicle can absolutely father children. The remaining testicle typically produces enough sperm and testosterone to support natural conception, and many men in this situation go on to have biological children without any medical assistance. The story gets more nuanced depending on why someone has a single testicle and what condition the remaining one is in, but the short answer is reassuring for the vast majority of men who find themselves with one.
How One Testicle Picks Up the Slack
When a man loses a testicle or is born with only one, the remaining testicle often undergoes a process called compensatory hypertrophy. It gradually enlarges and increases its output of both sperm and hormones to partially make up for the missing one. Research in boys with one undescended testicle shows that the descended testicle can grow larger than expected, and hormone-stimulation tests confirm that it responds robustly, producing normal peaks of reproductive hormones and a significant testosterone response when challenged.1PubMed. Unilateral cryptorchidism with compensatory hypertrophy of descended testicle in prepubertal boys
This compensation is not always perfect, though. A study comparing men with a solitary testicle to men with two found that testosterone levels were essentially the same between the groups, with median values landing right around 380 to 390 ng/dl. However, follicle-stimulating hormone (FSH), the hormone that drives sperm production, was higher in men with one testicle. That elevated FSH is the body’s way of pushing the single testicle harder to keep sperm output up. Interestingly, men with a solitary testicle could still produce sperm at FSH levels where men with two testes would have no sperm at all, suggesting the remaining testicle develops a kind of resilience.2PubMed. Evaluation of Reproductive Parameters in Men with Solitary Testis
One caveat: about 28% of men with a solitary testicle in that same study showed signs of “compensated hypogonadism,” meaning their testosterone levels looked normal on paper, but only because their bodies were working overtime with elevated luteinizing hormone to maintain that number. Compare that to roughly 8% in men with two testes. For most, this compensation works well enough that they feel fine and function normally. But it does suggest the hormonal system is running with less margin, which can matter as men age.2PubMed. Evaluation of Reproductive Parameters in Men with Solitary Testis
Sperm Counts and What They Mean for Conception
Sperm counts in men with one testicle tend to be lower than population averages, but “lower” does not mean “too low.” A comparative study of men who had lost a testicle to orchidectomy (surgical removal) found that roughly half had sperm concentrations below 20 million per milliliter, which is around the threshold that fertility specialists traditionally use as a benchmark. That proportion was similar across groups who lost a testicle for different reasons. But critically, a count below 20 million per milliliter does not mean infertility. Natural conception regularly happens at lower counts. It simply means that, statistically, it may take longer to conceive or that the odds per cycle are somewhat reduced.3PubMed. Comparative study of the fertility potential of men with only one testis
The practical upshot is that most men with a single healthy testicle do not need fertility treatment. Many conceive without ever knowing their sperm count is on the lower side. If conception is not happening after a year of trying, a semen analysis is a reasonable first step, just as it would be for any couple experiencing difficulty.
Why You Have One Testicle Matters
Not every route to a single testicle carries the same fertility implications. The cause tells you a lot about how the remaining testicle is likely to perform.
Testicular Cancer
This is the most common reason young men end up with a solitary testicle. Testicular cancer typically strikes between ages 15 and 35, and the standard first step is radical orchiectomy, the removal of the affected testicle. The surgery itself does not damage fertility in the remaining testicle. The bigger concern is what comes after. Radiation therapy and certain chemotherapy regimens can temporarily or permanently impair sperm production in the remaining testicle. A study of testicular cancer patients found that recovery of sperm production after radiation depended on the dose received, that chemotherapy added to the recovery time, and that men who already had lower sperm counts before treatment recovered more slowly.4PubMed. Long-term recovery of spermatogenesis after radiotherapy in patients with testicular cancer
For many men, sperm production does bounce back months to years after treatment ends. But the uncertainty is real, which is why sperm banking before any treatment begins is strongly recommended. More on that below.
Undescended Testicle
Some men are born with one testicle that never descended into the scrotum, a condition called cryptorchidism. If the undescended testicle is surgically brought down early in life (ideally before age two), the fertility outlook is much better. Even so, fertility is somewhat reduced compared to the general population. Reported paternity rates for men with a history of one undescended testicle land around two-thirds, compared to less than one-third for men who had both testicles undescended.5PubMed Central. Undescended testicle: An update on fertility in cryptorchid men Men with bilateral cryptorchidism face about a sixfold greater risk of infertility compared to those with one-sided disease or the general population.6PubMed Central. Cryptorchidism and Fertility
The reduced fertility in cryptorchidism is not solely about having fewer testicles. The condition itself is associated with underlying differences in testicular development that can affect sperm quality even in the testicle that descended normally. That is part of why the paternity rate, while encouraging, is not quite as high as you might expect for men who still have one functioning testicle.
Testicular Torsion
Torsion happens when a testicle twists on its blood supply, cutting off circulation. If surgery does not untwist it in time, the testicle may need to be removed. The fertility picture after torsion is a bit muddled in the research. Some animal and human studies have suggested that torsion in one testicle can trigger an immune response that damages the other testicle as well, because the blood-testis barrier gets disrupted.7PubMed Central. The Impact of Testicular Torsion on Testicular Function However, clinical studies in humans have not consistently confirmed reduced fertility after unilateral torsion, with at least one study reporting outcomes that contradicted the earlier experimental findings.8PubMed Central. Effect of unilateral testicular torsion at different ages on male fertility
In practice, most men who lose one testicle to torsion retain fertility through the remaining one. The theoretical risk of contralateral damage is worth being aware of, and a semen analysis after recovery can put any worries to rest.
Trauma
Severe injury to a testicle, from sports, accidents, or other causes, occasionally requires removal. When the remaining testicle is healthy and was not injured in the same event, fertility prospects are generally good. Even in extreme cases where a solitary testicle is severely injured, surgical repair can sometimes preserve function. A case report documented repair of a “shattered” solitary testicle that went on to function satisfactorily afterward, highlighting how aggressively surgeons will work to save a sole remaining testicle.
Sperm Banking Before Treatment
If you are about to have a testicle removed and the reason is cancer, banking sperm beforehand is one of the most straightforward and impactful decisions you can make. It takes a single visit to a fertility clinic, the sample is frozen and stored, and it provides an insurance policy against the possibility that chemotherapy or radiation affects your future fertility.
The utilization rates for banked sperm are actually quite low. Studies of men who banked sperm before cancer treatment found that fewer than 10% ever came back to use it for fertility treatment.9PubMed Central. Sperm Cryopreservation before Testicular Cancer Treatment and Its Subsequent Utilization for the Treatment of Infertility That is actually good news: it means the vast majority recovered enough fertility naturally that they did not need the frozen sample. But for the small percentage who did need it, having that backup made the difference between being able to have biological children and not.
One important timing detail: ideally, sperm should be collected before the orchiectomy itself, not just before subsequent chemotherapy. A case report described a patient with a testicular tumor who was already producing very low sperm counts, and after the affected testicle was removed, he had no sperm suitable for freezing at all. Because nobody had checked his semen quality before the first surgery, the window for banking had closed by the time chemotherapy was needed.10PubMed. Benefit of sperm freezing before radical orchiectomy The lesson: if orchidectomy is on the table, ask about a semen analysis and banking before the operation, not after.
When Assisted Reproduction Comes Into Play
For the minority of men with a single testicle who do end up with severely impaired sperm production, modern reproductive medicine offers options. If no sperm appear in the ejaculate at all, a procedure called micro-TESE (microsurgical testicular sperm extraction) can sometimes retrieve sperm directly from the testicle tissue. Those sperm are then used for in vitro fertilization with a technique called ICSI, where a single sperm is injected directly into an egg.
The success rates are encouraging even in difficult cases. One large single-center study of men with no sperm in their ejaculate reported that when sperm was successfully retrieved and ICSI was performed, the live-birth rate reached about 43% in the first embryo transfer cycle and climbed to roughly 47% across cumulative cycles.11PubMed Central. Clinical Outcomes and Live Birth Rate Resulted From Microdissection Testicular Sperm Extraction With ICSI-IVF in Non-Obstructive Azoospermia These are not single-testicle-specific numbers, but they represent the population of men with the most severe sperm production problems, and they show that even a worst-case scenario does not mean parenthood is off the table.
Having only one testicle does not change the mechanics of micro-TESE, but it does raise the stakes. With two testes, surgeons can sample one and leave the other untouched. With one, the procedure is being performed on the only testicle available, so surgeons take extra care to minimize tissue damage. The microsurgical approach, which uses high magnification to identify the most promising areas of tissue, is particularly valuable in this setting.
Monitoring the Remaining Testicle Over Time
If the reason for losing a testicle was cancer, keeping close tabs on the remaining one is critical. A large study of over 1,800 men with testicular germ-cell tumors found that about 5% had pre-cancerous changes (called testicular intraepithelial neoplasia, or TIN) in the opposite testicle. Risk factors for this included a smaller-than-normal remaining testicle and a history of cryptorchidism. In patients who were found to have TIN and received targeted low-dose radiation to the remaining testicle, the abnormal cells were eliminated in every case.12PubMed. Management of contralateral testicular intraepithelial neoplasia in patients with testicular germ-cell tumor
The 5% figure is low enough that most men will never face this problem, but high enough that routine follow-up is warranted. Regular self-exams and periodic ultrasound checks can catch any changes early, when treatment is most effective and least likely to affect the remaining testicle’s function.
Beyond cancer surveillance, men with one testicle should be aware that conditions like varicoceles (enlarged veins around the testicle) can develop in the remaining testicle and potentially affect sperm production. Research has confirmed that microsurgical varicocele repair is both safe and effective in a solitary testicle, so treatment is available if needed.13PubMed Central. Subinguinal microsurgical varicocelectomy is safe and effective in a solitary testicle
Testosterone and Aging With One Testicle
One concern that comes up frequently is whether testosterone levels will hold up over the long term with just one testicle. As mentioned earlier, studies show that median testosterone levels in men with a solitary testicle are statistically indistinguishable from men with two. But the higher rate of compensated hypogonadism, where the body is working harder behind the scenes to maintain that normal level, suggests that the hormonal cushion is thinner.
All men experience a gradual decline in testosterone as they age, typically losing about 1 to 2 percent per year after age 30. Starting with less hormonal reserve could mean that symptoms of low testosterone, such as fatigue, reduced libido, or decreased muscle mass, show up somewhat earlier or more noticeably. This is speculative and varies widely between individuals, but it is a reasonable conversation to have with a doctor as you move into your 40s and 50s. Periodic testosterone checks can identify any decline early enough to intervene if needed.
The fertility window is less affected by this gradual decline than you might think. Men produce sperm throughout their lives, and while sperm quality does decrease with age, a man with one well-functioning testicle at 45 or 50 can still father children naturally in many cases. The more relevant question for older men with a single testicle is usually testosterone-related quality of life, not reproductive capacity per se.
Protecting Your Remaining Testicle
When you have only one testicle, the practical calculus around risk changes. An injury that would be painful but recoverable with two testes could be life-altering with one. Contact sports, cycling, and certain occupational hazards all deserve a second thought, not necessarily avoidance, but appropriate protection.
Athletic cups and protective gear are inexpensive and effective. Many men with a single testicle continue to play sports at every level, from recreational to professional, without issues. The key is habit: wearing protection consistently rather than assuming the odds of a direct hit are low enough to ignore. Some urologists formally recommend that men with a solitary testicle wear a cup during any contact sport, and some sports medicine organizations have echoed this advice.
Beyond physical protection, overall testicular health benefits from the same lifestyle factors that support fertility generally: maintaining a healthy weight, avoiding excessive heat exposure to the groin (like prolonged hot tub use or laptop-on-lap habits), limiting alcohol, and avoiding anabolic steroids, which suppress the body’s own testosterone and sperm production. With one testicle doing the work of two, you have less room for external factors that impair its function.
The Prosthetic Question
Many men who have lost a testicle are offered a testicular prosthesis, a silicone implant placed in the scrotum to restore a natural appearance and feel. This is a cosmetic decision that has no effect on fertility, hormone production, or sexual function. The remaining testicle does all the biological work regardless of whether a prosthesis is present.
Some men find that a prosthesis reduces self-consciousness and improves body image, while others are indifferent or decide against the additional surgery. There is no medical reason to get one or to skip one. It is purely about personal comfort. If you are considering it, the procedure is typically straightforward and can be done at the time of orchiectomy or as a separate surgery later.