Over a 3-year period 51 patients with urethral strictures were treated by internal urethrotomy and then either randomly allocated to a course of post-operative dilatation or no dilatation. The patients in the self-intermittent dilatation (SID) group were shown how to pass a 16-F catheter through the stricture but not into the bladder. Complete follow-up was available in 44 patients, 32 of whom had new strictures while 12 had recurrent strictures. Of the patients with new strictures 13 (76%) in the SID group and 12 (80%) in the non-SID group achieved a satisfactory result (a flow rate > 12 ml per second) at one year (chi 2 = 0.18, P = 0.67). In the 12 patients with recurrent strictures 4 (66%) patients in the SID group and 1 (17%) patient in the non-SID group achieved a satisfactory result (chi 2 = 3.09, P = 0.079). In both groups results were not statistically significant. The technique of short-term postoperative self-dilatation does not seem to prevent recurrent strictures in patients treated with internal urethrotomy.