Acute urinary retention was relieved by simple transurethral emptying of the bladder in 107 men. In a group of 70 men with either diagnosed or assumed benign hyperplasia of the prostate, 70% (45/64) had repeat retention within one week and in only 16% (11/68) was micturition unaffected during the observation period of five years. Definitive treatment of the underlying disease was performed mainly during the first six months. The prognosis in benign prostatic hyperplasia was independent of patient age, volume of retained urine or previous occurrence of retention. It is concluded that acute urinary retention is a powerful indication for definitive treatment in prostatic disorders and that simple mechanical emptying of the bladder is unacceptable without subsequent observation.