Congenital or acquired defects in the mesentery are rare, and defects of the supporting structures and in the peritoneum of the pelvis are even more uncommon. Such pelvic peritoneal defects have been associated with endometriosis; however, the extent of this association has been unclear. In the present study, 309 patients had a diagnostic laparoscopy performed for pelvic pain in a prospective manner over a 2-year period. A total of 53 patients were found to have pelvic peritoneal defects. Seventy-nine percent of this group with peritoneal defects had associated endometriosis. Of the 309 patients undergoing laparoscopy, 148 patients were diagnosed as having endometriosis. Twenty-eight percent of this group with endometriosis had pelvic peritoneal defects. We conclude that when such defects are found at laparoscopy, the presence of endometriosis should be investigated thoroughly.