Causes of post-prostatectomy retention.
 Forty-eight patients in urinary retention following prostatectomy underwent urodynamic evaluation.
 Fifteen patients (31%) were found to have persistent residual obstruction, while 14 patients (29%) had detrusor hyporeflexia.
 In 9 patients (19%) a combination of outflow obstruction and detrusor hyporeflexia was demonstrated.
 In 6 patients (13%), urinary retention was due to compromised mental status.
 No abnormality was detected in remaining 4 patients (8%) on urodynamic evaluation.
 For proper evaluation of unsatisfactory voiding after prostatectomy cystoscopy is of limited value while urodynamic testing is essential.
