We found elevations of plasma dehydroepiandrosterone-sulfate (DHAS) in five boys, 5.5 to 10.3 years of age (group A), with premature pubarche (pubic hair development) or acne as an isolated phenomenon. Four boys (group B) with seemingly idiopathic premature pubarche (DHAS normal for age) were discovered to have above-average dehydroepiandrosterone levels. All of these boys with premature pubarche had some evidence of cerebral dysfunction or were obese. Plasma testosterone values and bone age were not markedly increased in either group. In each case studied, the patterns of plasma steroid intermediates before and after administration of adenocorticotropin were typical of adrenarche rather than of congenital adrenal hyperplasia or Cushing syndrome. In addition, DHAS was dexamethasone suppressible, and in those patients in whom nocturnal testosterone sampling or gonadotropin-releasing hormone testing was performed, no evidence of true puberty could be found. Fifteen percent of our normal male volunteers over 10 years of age developed pubarche with plasma DHAS levels over 120 micrograms/dl without evidence of true puberty. Thus pubarche as an isolated phenomenon does not necessarily indicate a virilizing disorder or true puberty. In the majority of cases, isolated pubarche appears to be the result of isolated adrenarche, the maturational increase in adrenal production of 17-ketosteroids.