Patient positioning is of critical importance in the successful performance of several radical pelvic operations. Adequate exposure of the prostatic apex is vital in ligating the dorsal vein complex and performing vesicourethral anastomosis. To test the effect of different patient positions on urethral mobility, we conducted a prospective controlled study measuring the relative cephalad displacement of the prostatic apex in 3 positions, that is the supine, frog-leg and dorsal lithotomy positions. A combination of radiographic and cystoscopic techniques was used to mark the position of the prostatic apex. Each patient served as his own control. Of the 24 patients studied for a variety of urological complaints 19 (79%) had an increased cephalad displacement of the prostatic apex while in the frog-leg position compared with the dorsal lithotomy position. The mean gain was 0.5 cm. (p greater than 0.5). A total of 16 patients showed improvement while in the frog-leg position over the supine position with a mean advantage of 0.39 cm. (p greater than 0.05). Patient age, pelvic depth, pelvic circumference and prostatic urethral length had no predictive value in selecting an optimal position.