Urodynamic evaluation was performed in 13 men 4 to 18 months after cystoprostatectomy and bladder replacement using a detubularized right colonic segment. All patients are continent by day and only 3 are incontinent during the night to a degree that necessitates use of a condom catheter. Two patients awaken every 2 to 3 hours to void and the remainder have nocturia comparable to normal men of their age. The residual volume was 0 to 70 ml. The urethral closure pressure was normal, and in 3 patients studied preoperatively and postoperatively no significant change was observed other than shortening of the profile length. Maximal flow rates were normal although the pattern was intermittent. In 2 patients no cystoplasty contractions were recorded and in all but 2 patients the amplitude of the contractions was less than 40 cm. water. Simultaneous bladder and urethral pressure recordings during bladder filling demonstrated no change in urethral pressure in 10 patients. Although creation of a reservoir with a low pressure and careful preservation of the infraprostatic urethra are important for continence in these patients, we believe that the absence of normal sacral route reflexes after cystoprostatectomy is an important contributing cause to nocturnal incontinence.