There is a strong suspicion among urologists that the prevalence of benign prostatic hyperplasia is higher than has been reported in clinical retrospective and necropsy studies. To find out the prevalence in one community all men aged 40-79 years registered with a group general practice were invited to complete a urinary symptom questionnaire and to undergo uroflowmetry. 705 men (77% of those eligible) participated. 214 men (84% of those invited) with signs and symptoms of prostatic dysfunction subsequently underwent transrectal ultrasonography (TRUS) for assessment of the volume (and by inference weight) of their prostates. The prevalence rate of benign prostatic hypertrophy (BPH), defined as enlargement of the prostate gland of equivalent weight greater than 20 g in the presence of symptoms of urinary dysfunction and/or a urinary peak flow rate less than 15 ml/s and without evidence of malignancy, was 253 (95% CI 221-285) per 1000 men in the community, rising from 138 per 1000 men aged 40-49 years to 430 per 1000 men aged 60-69 years. Thus apparently well men have a much higher frequency of BPH than was previously thought to be the case.