Adenomyosis and endometriosis are not the same condition, but they are closely related. Both involve tissue similar to the uterine lining growing where it shouldn’t, and they share several symptoms, including pelvic pain and painful periods. The key difference is location: in endometriosis, that tissue grows outside the uterus, while in adenomyosis, it burrows into the muscular wall of the uterus itself. Despite being distinct diagnoses, the two conditions overlap so frequently that between 30% and 90% of people with endometriosis also have adenomyosis.
Where the Tissue Grows
The uterus has an inner lining (the endometrium) and a thick muscular layer beneath it (the myometrium). In adenomyosis, cells resembling the endometrial lining invade downward into the myometrium. This triggers a local inflammatory response and causes the muscle to thicken. Over time, the uterus often becomes enlarged and takes on a rounded, globular shape.
Endometriosis takes the opposite route. Endometrial-like tissue shows up outside the uterus entirely. Superficial endometriosis sits on the peritoneal surface, the thin membrane lining the pelvis. Deep endometriosis infiltrates further into pelvic structures like the bowel, bladder, or ligaments supporting the uterus, and it tends to form fibrotic, scar-like lesions. The tissue can also appear on the ovaries, forming cysts known as endometriomas. Because the disease is scattered across the pelvis rather than contained in one organ, it behaves differently and requires a different treatment approach.
Symptoms That Overlap and Diverge
Both conditions cause painful periods, chronic pelvic pain, and pain during sex. That overlap is a major reason many people assume they’re the same disease, and it’s also why getting an accurate diagnosis can take years.
Adenomyosis tends to produce heavier bleeding. People with adenomyosis are more likely to experience extremely heavy periods, pass large clots, bleed between periods, and develop symptoms of anemia from the ongoing blood loss. The enlarged uterus can also create a persistent feeling of fullness, pressure, or bloating in the lower abdomen, even outside of menstruation. Adenomyosis symptoms often occur all the time rather than flaring only around a period.
Endometriosis symptoms, by contrast, tend to track more closely with the menstrual cycle. Pain typically spikes during or just before a period and may ease between cycles. Depending on where the lesions are located, endometriosis can also cause pain with bowel movements, urination, or deep penetration during sex. Fatigue and gastrointestinal symptoms like bloating and nausea are common enough that endometriosis is sometimes mistaken for irritable bowel syndrome.
Who Gets Each Condition
The typical patient profiles differ, though there’s plenty of crossover. Endometriosis is often diagnosed in younger women and may be inversely linked to having had children. Adenomyosis is more commonly identified in middle-aged women and those who have previously given birth. One retrospective study found that patients with adenomyosis alone had a mean age around 39, while those diagnosed with both conditions averaged closer to 49. These are trends, not rules. Both conditions can affect people across a wide age range, and the high rate of co-occurrence means many patients don’t fit neatly into one category.
How Each Is Diagnosed
Endometriosis has historically been confirmed through laparoscopic surgery, where a surgeon visually identifies and biopsies lesions inside the pelvis. Increasingly, specialized ultrasound and MRI can detect deep endometriosis and ovarian endometriomas without surgery, but superficial disease remains difficult to see on imaging.
Adenomyosis is typically diagnosed through transvaginal ultrasound or MRI. Imaging can reveal characteristic features: an asymmetrically thickened uterine wall, tiny cysts within the muscle, and a poorly defined border between the lining and the muscle layer (known as the junctional zone). MRI can measure the thickness of that junctional zone, which helps confirm the diagnosis. Because the disease lives inside the uterine wall rather than scattered across the pelvis, it’s generally more straightforward to identify on imaging than endometriosis is.
How They Affect Fertility
Both conditions can make it harder to conceive, but they do so through different mechanisms. Endometriosis can distort pelvic anatomy, block fallopian tubes, damage egg quality, and create an inflammatory environment hostile to embryo implantation.
Adenomyosis primarily affects what happens after an embryo implants. A prospective study of IVF patients using donor eggs found that adenomyosis did not significantly reduce implantation or clinical pregnancy rates. However, miscarriage rates were roughly double: 35.4% in women with adenomyosis compared to 18.1% in those without. The location and severity of the disease mattered. When adenomyosis was detected in the junctional zone, the inner portion of the uterine muscle closest to the lining, miscarriage risk increased more than threefold. Diffuse or severe disease doubled the risk. Interestingly, when adenomyosis was limited to the outer muscle layer, ongoing pregnancy rates were actually higher.
For people trying to conceive, knowing which condition is present (or whether both are) helps fertility specialists tailor treatment. The two diagnoses create different obstacles, and managing one without recognizing the other can leave part of the problem unaddressed.
Why They So Often Occur Together
The co-occurrence rate is strikingly high. Systematic reviews estimate that 30% to 90% of people with endometriosis also have adenomyosis, and 60% to 80% of people with adenomyosis have co-existing endometriosis. Researchers are still working out whether this reflects a shared underlying cause, like hormonal or immune dysfunction, or whether one condition predisposes someone to the other. What’s clear is that if you’ve been diagnosed with one, there’s a meaningful chance the other is also present, which is worth discussing with your doctor, especially if symptoms don’t fully improve with treatment.
Treatment Differences
Hormonal treatments are a first-line option for both conditions. Birth control pills, progestin-based therapies, and hormonal IUDs can suppress the growth of endometrial-like tissue and reduce pain and bleeding regardless of where it’s located.
The surgical picture is where the two conditions diverge most sharply. Endometriosis lesions can be surgically excised from pelvic surfaces, but because the disease exists across multiple sites, surgery doesn’t guarantee a cure. Lesions can recur, and some may be missed. For adenomyosis, removing the uterus (hysterectomy) is considered definitive treatment because the disease is contained entirely within the uterine wall. Once the uterus is gone, adenomyosis cannot come back. That’s not the case for endometriosis, which can persist even after hysterectomy because lesions outside the uterus remain untouched.
For people who want to preserve fertility, conservative approaches like hormonal management and, in some endometriosis cases, excision surgery are the primary options. The choice depends on which condition is driving symptoms, how severe it is, and whether pregnancy is a goal.