Four hundred patients with benign prostatic hypertrophy (BPH) undergoing prostatic surgery were enrolled in this study in order to search for factors predictive of a successful outcome. 139 patients had acute urinary retention and the others had irritative and obstructive voiding symptoms. Preoperative examinations included intravenous urography (IVU), transrectal sonography of the prostate (TRSP), cystometry, uroflowmetry, and urethral pressure profilometry (UPP). Retropubic prostatectomy was undertaken in 16 cases, transurethral resection of the prostate in 335, and transurethral incision of the prostate in 49. In the follow-up period of 3 months to 3 years, a strictly successful result was achieved in 324 patients (81%). 26 patients (6.5%) had a fair result, 30 (7.5%) were stationary, in 18 (4.5%) the symptoms became worse, and 2 (0.5%) died postoperatively. On analysis of the success rate, 9 favorable factors and 9 unfavorable factors were noted. A symptomatic large prostatic adenoma proven by IVU, TRSP, or UPP will imply a higher success rate. Urodynamically obstructive BPH proven by a high voiding pressure and constrictive flow pattern can also predict a satisfactory outcome. The unfavorable factors always come from a small adenoma, uncertain irritative symptoms and detrusor underactivity. Patients with more than 2 unfavorable factors should be investigated carefully before surgery. The presence of 2 favorable factors without an unfavorable factor will usually predict the best surgical outcome.