Objectives. Intraoperative nerve stimulation has been used to map the course of cavernosal nerve bundles to aid in nerve-sparing radical prostatectomy (RP). We sought to determine whether the intraoperative nerve stimulation response after removal of the prostate specimen predicts postoperative potency. Methods. We prospectively evaluated 63 consecutive patients undergoing RP. Among these 63 patients, 41 patients had a bilateral nerve-sparing procedure, and 22 underwent bilateral wide resection of the neurovascular bundles. Potency was determined at I year by direct patient interview. Results. Of the 22 patients with wide resection, 16 (73%) had no observed stimulated response, 4 (18%) had a measurable tumescence response, and 2 (9%) had detumescence. All 22 patients were impotent postoperatively. At a minimum follow-up of 1 year, of the 41 patients who underwent nerve-sparing RP, 27 (66%) had postoperative erections sufficient for penetration. Of the 30 men with an intraoperative stimulated tumescence response, 24 (80%) were potent; of the 6 with a detumescence response, 2 (33%) were potent; and of the 5 with no stimulated nerve response, 1 (20%) was potent. A tumescence response was significantly more predictive of postoperative potency than no intraoperative response (P = 0.017). Conclusions. An intraoperative tumescence response with stimulation of the neurovascular bundles after prostate specimen removal is more likely to correspond to successful postoperative sexual function after nerve-sparing RP than is no response. (C) 2001, Elsevier Science Inc.