Among 60 spinal cord injury patients who underwent external urethral sphincterotomy 45 experienced success and 15 failed. Failure was established when symptomatic urinary tract infections and high vesical residuals persisted. Urodynamic findings demonstrated detrusor areflexia in 10 patients (66 per cent), detrusor-sphincter dyssynergia in 2 (13.2 per cent), detrusor hyperreflexia with unsustained bladder contractions in 1 (6.6 per cent), and detrusor hyperreflexia and bladder neck obstruction in 2 (13.2 per cent). Among these failures poor detrusor contractility predominated. Detrusor-sphincter dyssynergia may indicate an inadequate surgical relief of obstruction. Bladder neck obstruction may indicate that a bladder neck incision should be considered when an external sphincterotomy is performed.