Endoscopic pelvic lymph node dissection was performed in 30 patients as part of the staging of prostate (19) or bladder (11) cancers. The technique, using a procedure of detachment of the retroperitoneal space with CO2 insufflation, is described. Complete bilateral dissection of the ilio-obturator lymph nodes was performed in 24 patients (80%) using conventional laparoscopic surgical equipment. Only a unilateral dissection could be performed in 6 other patients because of technical difficulties. The mean operating time was 72 minutes. The intraoperative and postoperative complications consisted of 2 venous injuries and one infection. A prospective study of systemic diffusion of CO2 demonstrated that the blood Co2 level increased significantly during the procedure, but could be controlled by adaptation of the ventilation. Postoperative monitoring of blood CO2 levels using a capnograph is recommended. 4 out of 30 patients (13%), 2 with prostate cancer and 2 with bladder cancer, had lymph node metastases. Amongst the other 26 patients, 12 were treated by radiotherapy (bladder cancer), 12 patients underwent perineal prostatectomy and 12 others underwent retropubic prostatectomy (5) or prostatocystectomy (7]). No intraoperative and postoperative morbidity related to endoscopic lymph node dissection was observed in the patients subsequently undergoing a radical operation. Endoscopic retroperitoneal lymph node dissection with CO2 insufflation is a rapid, safe and effective technique for staging of malignant pelvic tumours and constitutes an alternative to open surgery and to endoscopic transperitoneal surgery.