In some women, endometrial mucosa is found outside the uterus in the abdominal cavity. It is observed in the ovaries, on the Fallopian tubes, the bladder and on the intestines. The most frequent symptom is abdominal pain just before menstruation begins. Endometriosis can also cause blood cysts inside the ovaries.

Endometriosis is more frequently found in infertile compared to fertile women. However, it is not proven that endometriosis is the reason for infertility in affected women. For some reason women with endometriosis have reduced pregnancy chances with insemination, and IVF is often recommended instead.