11 beta-hydroxylase deficiency in hyperandrogenism. OBJECTIVE: to determine the 11-deoxycortisol (S) response and incidence of 11 beta-hydroxylase deficiency in hyperandrogenism. DESIGN: Hyperandrogenic women prospectively and consecutively underwent acute adrenal stimulation studies. SETTING: Tertiary institution. PATIENTS: Two hundred sixty women complaining of hirsutism and/or hyperandrogenic oligomenorrhea were studied, excluding five unrelated families (1.9% of total) suffering from 21-hydroxylase deficient late-onset adrenal hyperplasia. Forty-one healthy premenopausal eumenorrheic women served as controls. MAIN OUTCOME MEASURES: Only two unrelated women (0.8%) had a poststimulation or net increment S level value greater than or equal to threefold the upper 95th percentile of controls and were presumed to suffer from 11 beta-hydroxylase deficient late-onset adrenal hyperplasia. One hundred nine (42%) of hyperandrogenic women had at least one S value above the 95th percentile of controls. These women also demonstrated higher basal (F0) and stimulated cortisol levels, but a similar increment compared with controls. RESULTS: Patients with high S measures had higher testosterone, dehydroepiandrosterone sulfate, and androstenedione levels, but similar luteinizing hormone/follicle-stimulating hormone ratios, than hyperandrogenic cohorts with no abnormal S measures. Basal values of S (S0), F0, or S0/F0 were not useful to predict an abnormal S response to stimulation. CONCLUSIONS: Although adrenocortical hyperactivity was present in 42% of our hyperandrogenic patients, only 0.8% were presumed to suffer from 11 beta-hydroxylase deficient late-onset adrenal hyperplasia. A systemic search for this deficiency in hyperandrogenism is probably unwarranted. 