The objective of this work was to assess the advantages and the role of rectal endoscopic ultrasonography (EUS) when establishing evidence of infiltration of the rectal wall in patients with proven deep pelvic endometriosis. To this end we performed a retrospective study between July 1993 and December 1996 of a continuous series of 38 patients who presented with deep pelvic endometriosis which was confirmed histologically. The EUS results were considered normal in nine cases (23.7%). In 12 cases (31.6%) EUS revealed an image compatible with infiltration of the uterosacral ligaments and/or the rectovaginal septum without any associated bowel infiltration. In 17 cases (44.7%) EUS revealed an image compatible with deep infiltration of the intestinal wall. Sixteen of these 17 patients underwent laparotomy with bowel resection. The histological results confirmed in each of these 16 patients (100%) that there was deep infiltration of the intestinal wall by endometriotic lesions. The seventeenth patient refused such major surgery by laparotomy, and underwent partial laparoscopy due to the risk of bowel injury. For the 21 patients with no EUS evidence of rectal infiltration complete laparoscopic surgical exeresis was achieved in every case (100%) without broaching the intestinal wall. These preliminary results enable us to state that EUS, which is a simple and non-invasive technique, provides a reliable indication as to the presence of deep bowel infiltration in patients with retroperitoneal endometriotic lesions. EUS used pre-operatively enables patients to be selected for treatment via laparotomy or by laparoscopic surgery.