PCOS vs Endometriosis: Different Diseases, Overlapping Symptoms

Is it PCOS, endometriosis, or both?

Roughly 1 in 8 women has PCOS, and up to 1 in 10 has endometriosis, and the two get confused constantly because three symptoms overlap almost completely: irregular or painful periods, pelvic discomfort, and trouble conceiving. Past that overlap, the diseases have almost nothing in common.

PCOS is a hormonal and metabolic condition. Excess androgens and, in most phenotypes, insulin resistance interfere with the signal that tells an ovary to release an egg, which is why cycles go long, unpredictable, or absent. Endometriosis is a structural and inflammatory disease: tissue that resembles the uterine lining grows outside the uterus — on the ovaries, the peritoneum, sometimes the bowel or bladder — and bleeds and inflames in step with the menstrual cycle whether or not ovulation is normal. Endometriosis is reliably confirmed only through surgical visualisation, while PCOS is diagnosed from blood tests, a pelvic ultrasound, and a symptom pattern — already a clue that these are not variations on one disease.

Note: in May 2026, PCOS was renamed polyendocrine metabolic ovarian syndrome, or PMOS, by a global consensus of more than 50 organisations. Same condition, same mechanism — only the label changed. This article uses PCOS, since that is still the term most readers search.

What actually separates them, feature by feature

The two conditions fail almost every comparison point except the three symptoms that cause the confusion in the first place. PCOS is diagnosed against the Rotterdam criteria — two of three specific findings, applied only after other causes are ruled out — while endometriosis has no equivalent points-based rule.

PCOS vs endometriosis symptoms: where the overlap is real

Three symptoms genuinely overlap, and the rest of the picture usually does not.

Cycle length is the clearest split. PCOS cycles are irregular because ovulation itself is unreliable — cycles can run 35, 60, or 90 days apart, or stop for months. Endometriosis rarely changes cycle length; periods typically arrive on schedule but are heavier, longer, or markedly more painful than before. A person tracking cycle length alone is tracking the PCOS signal, not the endometriosis one.

Pain is the second split, and it runs the other way. PCOS does not reliably cause pelvic pain — when it does, it is usually from an ovarian cyst rather than the condition itself, and what that ovary-specific pain actually feels like, plus the emergency signs that rule out torsion, is worth checking against on its own. Endometriosis pain is progressive: it often starts before a period, intensifies during it, and can extend to pain during sex or bowel movements as lesions accumulate over years. Endometriosis pain and cramps without an accompanying bleed have their own diagnostic pattern, and that pattern is worth checking against directly if pain — not cycle irregularity — is the dominant complaint.

The third split is androgen signs. Acne along the jawline, coarse dark hair on the chin or chest, and thinning at the crown point toward PCOS, because androgen excess is part of its definition. Endometriosis does not raise androgens, so a person with textbook endometriosis and no hormonal skin or hair changes is not thereby ruled in for PCOS — those are two separate questions, not one sliding scale.

Weight and metabolic signs split the same way, and this is where phenotype matters. Several PCOS phenotypes carry insulin resistance, which shows up as skin tags, velvety darkened skin at the neck or underarms (acanthosis nigricans), or weight concentrated around the waist. Endometriosis carries no comparable metabolic signature — body weight has little documented bearing on lesion severity or symptom intensity in the literature. A person with lean PCOS and no insulin resistance will not show this sign either, which is why it rules a symptom in rather than ruling a whole condition out.

Endometriosis or PCOS: the test that actually answers the question

For PCOS, the 2023 international guideline specifies a blood panel — total or free testosterone, LH and FSH — plus a pelvic ultrasound counting follicles or an anti-Müllerian hormone level as an alternative, applied only after other causes of the same hormone pattern have been excluded. No single test confirms PCOS; the diagnosis is a combination reached by ruling other things out first.

For endometriosis, the picture has shifted. The 2022 ESHRE guideline directly challenges laparoscopy and histology as the mandatory gold standard, recommending that clinicians can begin treatment based on history, examination, and imaging — transvaginal ultrasound or pelvic MRI — without waiting for surgical confirmation in a typical presentation. That said, imaging has real limits: it reliably detects an endometrioma or deep infiltrating disease but frequently misses superficial lesions, so a normal scan does not rule endometriosis out. Surgical visualisation with histological confirmation remains the only fully definitive test, reserved for cases where the diagnosis stays unclear or surgery is already planned for another reason.

In practice: a hormone panel and ultrasound answer the PCOS question in one visit. Answering the endometriosis question can mean starting treatment on clinical suspicion and only reaching a laparoscopy if that treatment fails or fertility surgery becomes the next step.

Can you have PCOS and endometriosis at the same time?

Yes, but a large 2024 study found it happens less often than the symptom overlap would suggest. In a nationwide cohort of 157,662 Korean women aged 15 to 45, researchers compared the health conditions clustering around a PCOS diagnosis against those clustering around an endometriosis diagnosis. PCOS and endometriosis affect a similar age group, yet the two rarely co-occurred and carried distinct comorbidity patterns rather than compounding each other: PCOS tracked with metabolic conditions — dyslipidaemia, type 2 diabetes, pregnancy-related complications — while endometriosis tracked with pain-related diagnoses and benign reproductive-organ growths. Infertility was one of the few findings significantly linked to both — trying to conceive with both conditions present pulls the work-up two ways, since ovulation induction and laparoscopy address different halves of the picture.

That distinction matters for a practical reason: having one does not make the other more likely, so a PCOS diagnosis is not a reason to assume endometriosis explains new pain, and an endometriosis diagnosis is not a reason to assume PCOS explains irregular cycles. Each needs its own evidence. For anyone managing both at once, the overlap between a PCOS diet and an endometriosis diet is narrower than either camp implies — the two bodies of evidence agree on less than they appear to.

PCOS is a diagnosis of exclusion — here is exactly what that does and does not include

The 2023 international guideline is explicit that PCOS cannot be diagnosed until other conditions producing the same hormone pattern — hyperandrogenism plus irregular ovulation — have been ruled out first: thyroid dysfunction, hyperprolactinaemia, non-classic congenital adrenal hyperplasia, and, when the picture fits, rarer causes such as Cushing’s syndrome or an androgen-secreting tumour. High prolactin produces a similar irregular-cycle picture and sits on that same exclusion list.

Endometriosis is not on that list, because it does not raise androgens or otherwise mimic the hormone pattern the guideline is screening for. That is precisely why it causes so much confusion in practice: it is not something your PCOS work-up rules out, so having a confirmed PCOS diagnosis tells you nothing about whether endometriosis is also present. If pelvic pain does not fit the PCOS picture, it needs its own evaluation rather than being filed under an existing diagnosis.

When your pattern does not fit either box cleanly

Neither of these conditions is the answer for everyone whose cycles are irregular or whose pelvis hurts. Adenomyosis, pelvic inflammatory disease, ovarian cysts unrelated to PCOS, irritable bowel syndrome, and interstitial cystitis can each produce pieces of this picture without being either PCOS or endometriosis. A normal testosterone panel and a normal pelvic scan do not mean nothing is wrong; they mean the next step is a different specialist’s territory, most often gastroenterology or urogynaecology depending on where the pain sits. This article does not replace that work-up — it exists so you know which two possibilities to ask about first, and which tests separate them.

Your next step

Track two things separately for one full cycle: how many days between periods, and whether pain starts before bleeding and builds through it. The first pattern is the PCOS question; the second is the endometriosis question. Bring both to your GP or gynaecologist along with a request for the same starting panel — testosterone, LH, FSH, and a pelvic ultrasound — since that single visit answers the PCOS half of the picture regardless of what else is going on. For what the full PCOS work-up covers and in what order, see the diagnosis hub.