The patterns and frequency of diurnal urination were studied in 412 male and 244 female participants in the Baltimore Longitudinal Study of Aging. Men urinated less often (mean 4.8 voids per day) than women (mean 5.6 voids per day). There was no main effect for age decade. However, an age by sex interaction showed that voiding in men increased across the decades and in women it decreased. The highest frequency was found in women in their 30s (mean 6.2) and the lowest was in men in their 30s (mean 4.3). Men and women in the 70 and older age group had the same voiding frequency (mean 5.0). In men frequency of urination was related to benign prostatic enlargement and 2 of 4 symptoms of urinary obstruction (change in the force of the urinary stream and having to urinate again shortly after voiding). In women frequency was related negatively to a history of pregnancy complications but not to parity. In both sexes frequency was unrelated to the reported daily ingestion of coffee, tea or diuretics, and no relationships were found with a history of an anxiety disorder.