Data from the United States Health Examination Survey, Cycle III, were used to describe secondary sexual characteristics and their relationship to skeletal age in a representative sample of adolescent males aged 12 to 17 years. This survey utilized a national probability sample of youths selected to represent the U.S. population with respect to age, race, sex, geographic region, and socioeconomic status. Good concordance was found between Tanner stages for pubic hair and for genitalia. Sexual characteristics developed similarly for white and black boys, and socioeconomic status did not influence this development. Skeletal age and serum urate levels were closely related to development of pubic hair and genitalia. These data permit the physician to compare the development of individual patients with a representative sample of contemporaneous U.S. boys.