Urodynamic evaluation was performed in 10 patients after radical cystoprostatectomy and continent urethral diversion with detubularized ileum and in 13 patients continent after radical prostatectomy. In both groups surgical techniques were modified to optimize preservation of the periurethral tissue at the prostatic apex. For the ileal neobladder group 9 patients (90%) were completely continent and 1 (10%) noticed moderate nocturnal incontinence. The urethral sphincteric mechanism was well preserved in these patients, with no significant difference between the 2 groups in mean functional urethral length (3.8 +/- 0.6 versus 3.6 +/- 0.8 cm., p = 0.55) or maximal urethral closure pressure (87 +/- 34 versus 74 +/- 20 cm. water, p = 0.26). Tubularization of the bladder or neobladder above the level of the external sphincter was noted in both groups. Continence after radical cystoprostatectomy with continent urethral diversion and after radical prostatectomy is dependent upon an intact urethral sphincteric mechanism as well as a compliant, low pressure reservoir, either bladder or a bladder substitute. Urinary incontinence after total bladder replacement with detubularized ileum can be minimized by preserving as much of the distal urethral sphincter as possible. This can be done by careful dissection of the prostatic apex, performed under direct vision, with an understanding of the anatomy of the urethral sphincter and its innervation.