The most common site for endometriosis is the:

Endometriosis most commonly affects the ovaries, where ectopic endometrial tissue forms cystic lesions called endometriomas. These lesions often cause inflammation, fibrosis, and adhesions, leading to chronic pelvic pain and infertility. During surgery, careful dissection of ovarian cysts and preservation of healthy ovarian tissue are critical to maintain fertility. The ovary’s rich blood supply and hormone responsiveness make it the predominant site for implantation and growth of endometrial implants. Identifying and excising ovarian endometriomas is a key surgical step to reduce symptoms and prevent recurrence.

Reference: Williams Gynecology, Hoffman et al., 3rd Edition.