To preoperatively predict follicular loss after laparoscopic cystectomy of ovarian endometriomas. Case-control study. (Canadian Task Force classification II-2). University hospital. Seventy-six women with ovarian endometrioma and 41 patients with nonendometriotic ovarian cysts who underwent laparoscopy. Sonographic findings and serum levels of CA 125 and CA 19.9 were recorded. Considered parameters were compared with a histologic score, on the basis of the presence and morphologic features of follicles on the normal ovarian tissue adjacent to the cyst wall surgically removed. Serum levels of CA 125 and CA 19.9 were increased in patients with ovarian endometrioma (p <.001 and p <.01, respectively). Capsule wall thickness, presence of fibrosis, and follicles in the tissue surrounding the capsule were significantly increased in the study group (p <.01). CA 125 serum level was directly correlated to the histologic score (r = 0.46, p <.05) and to cyst diameter (r = 0.12, p = .01), whereas no correlation was found between CA 19.9 or cyst diameter and follicular score. Our data suggest that the ovarian tissue inadvertently removed along with the endometrioma wall by laparoscopic stripping is due to pericystic fibrosis. Serum levels of CA 125 represent a useful parameter to predict follicular loss before surgery.