Balloon dilatation of the prostatic urethra may improve the uroflow in patients with benign prostatic hypertrophy (BPH). In this study, patients were assigned blindly for balloon dilatation (5 men) or observation (3 men). A 36F balloon was inflated in the prostatic urethra with local anesthesia and fluoroscopic guidance for thirty minutes. The effects of the procedure were monitored during a two-year follow-up period. Two of the treated patients had improvement in uroflow and experienced stabilization of clinical symptoms. Two had no significant change in uroflow and required prostatectomy within the observation period. One required prostatectomy soon after dilatation. One of the 3 patients in the control group required prostatectomy in the two-year follow-up period and the other 2 continue to have obstructive symptoms. Although dilatation of the prostatic urethra by balloon may relieve some patients of urinary outflow obstruction due to BPH, it appears that a 36F balloon dilator does not produce dramatic or consistent results, and the effects of larger balloons should be evaluated.