OBJECTIVE: Deficient adrenocortical 3β-hydroxysteroid dehydrogenase activity has been reported in 5% to 30% of hyperandrogenic women. Our objective was to determine the incidence and degree of 3β-hydroxysteroid dehydrogenase deficiencies in hyperandrogenism. STUDY DESIGN: A prospective study of adrenal function in patients with hyperandrogenism was performed in a tertiary care university medical center. Eighty-six consecutive patients with hirsutism or hyperandrogenic oligomenorrhea were studied; 26 healthy eumenorrheic women served as controls. All subjects underwent serum sampling at rest and a 1-hour adrenal stimulation test with 1 mg of intravenously corticotropin-(1-24). Dehydroepiandrosterone sulfate, androstenedione, sex hormone—binding globulin, total and free testosterone, and luteinizing and follicle-stimulating hormones were measured in basal serum; dehydroepiandrosterone, 17-hydroxyprogesterone, and 17-hydroxypregnenolone were measured in basal and corticotropin-stimulated serum. On the basis of experience with genetically defined 21-hydroxylase late-onset adrenal hyperplasia, patients were presumed to suffer from 3β-hydroxysteroid dehydrogenase—deficient late-onset adrenal hyperplasia if they demonstrated a dehydroepiandrosterone or 17-hydroxypregnenolone response to corticotropin-(1-24) stimulation (absolute poststimulation level or net increment) greater than threefold the upper 95th percentile of controls. RESULTS: Three women of two families (2.3%) had a 17-hydroxyprogesterone response consistent with 21-hydroxylase-deficient late-onset adrenal hyperplasia and were excluded from further study. Eighteen (21 %) of the remaining patients had a 17-hydroxypregnenolone poststimulation increment above the upper 95th percentile of controls (13.9 nmol/L), and two had an elevated dehydroepiandrosterone increment (〉 19.5 nmol/L). However, no patient exceeded threefold the upper control limit for either steroid response. Patients with an exaggerated dehydroepiandrosterone or 17-hydroxypregnenolone increment had higher circulating dehydroepiandrosterone sulfate levels but similar basal total and free testosterone, sex hormone--binding globulin, luteinizing and follicle-stimulating hormone concentrations, basal or stimulated androstenedione, dehydroepiandrosterone/androstenedione, and 17-hydroxypregnenolone/17-hydroprogesterone than their less responsive counterparts. CONCLUSIONS: Although an exaggerated response of 17-hydroxypregnenolone to adrenal stimulation is common in hyperandrogenism, a response severe enough to merit consideration as 3β-hydroxysteroid dehydrogenase—deficient late-onset adrenal hyperplasia was not encountered in this unselected patient population, suggestive of the rarity of this disorder. © 1993, Mosby. All rights reserved.