The present study included 118 patients undergoing a laparoscopy for infertility. In 86 patients with laparoscopically diagnosed endometriosis (group I), biopsies were taken from areas of apparent endometriosis (n = 86) and from a visually normal peritoneum (n = 52). Histology reveals the presence of endometriosis in 93% of positive sites and in 13% of negative sites. In 32 patients without endometriosis at laparoscopy (group II), biopsies were taken from normal uterosacral ligaments (n = 32). Endometriosis was observed in 6% of cases. Despite the increased ability to detect pigmented and nonpigmented endometriotic lesion, histological study revealed the presence of endometriosis in normal peritoneum in 13% (group I) and 6% (group II) of cases.