A controlled study of the effect of treatment of recurrent urethral stricture by internal urethrotomy followed by clean intermittent self-catheterization for 3 months is reported. There were 28 men (median age 70 years, range 18 to 75) allocated to internal urethrotomy and clean intermittent self-catheterization for 3 months (treatment group) and 33 (median age 76 years, range 36 to 87) were randomized to undergo internal urethrotomy only (observation group). The groups were comparable in terms of patient age, etiology of the primary stricture, number of recurrences, length and site of the actual stricture, and preoperative maximum flow rate (p less than 0.01). After termination of the treatment all patients from both groups were evaluated by uroflowmetry 2, 4, 6 and 12 months later, and a new recurrence was defined as a maximum flow rate of less than 10 ml. per second (micturition volume greater than 100 ml.) and a characteristic flow curve. From the treatment group 23 patients could be assessed: 2 had discontinued clean intermittent self-catheterization due to urethral hemorrhage, 2 died during the observation period and 1 was lost to followup. From the observation group 28 patients were assessable: 3 died during the observation period and 1 was lost to followup. Treatment results were not significantly different (p less than 0.01). Of the patients in the treatment and observation groups 78% and 82%, respectively, had a new stricture. The median interval for this to occur was 4 months for both groups. Since no patient had clinical signs of stricture during clean intermittent self-catheterization, we conclude that for the treatment of recurrent urethral stricture clean intermittent self-catheterization following internal urethrotomy should be continued for a long duration, possibly permanently.