A series of 273 consecutive patients with the primary complaint of pelvic pain were laparoscopically diagnosed as having endometriosis. Peritoneal and/or ovarian biopsy was performed at the endometriosis site or sites in 115 patients. Histologic confirmation of endometriosis was established in 64% of those patients. The severity of the disease did not correlate with positive or negative biopsy results. Thus, the diagnosis of endometriosis may not be histologically confirmed, even in the presence of grossly visible disease. Therefore, diagnosis and treatment of the disease should not depend upon histologic confirmation.