The natural history of prostatism (clinically diagnosed benign prostatic hyperplasia) is examined based on symptom questionnaires and digital rectal examinations administered periodically to 1,057 men followed prospectively for up to thirty years in the Baltimore Longitudinal Study of Aging (BLSA). Benign prostatic hyperplasia (BPH) was clinically diagnosed in 527 men, 110 had a prostatectomy for BPH, and in 21 prostate cancer developed. Among men aged sixty or older with prostatic enlargement and obstructive symptoms, the twenty-year probability of surgery was 39 percent; for men aged fifty to fifty-nine years this probability was 24 percent; and for men aged forty to forty-nine years, the probability was 13 percent. The age-specific prevalence of clinically diagnosed BPH agreed closely at all ages with the age-specific autopsy prevalence of pathologically defined BPH from a published international compilation of 5 independent autopsy studies involving 1,075 prostates.