Endocrine dysfunction was studied in 109 consecutive female patients with moderate to severe alopecia, mostly of a diffuse pattern. The study included an evaluation of associated hirsutism and/or menstrual dysfunction, plasma hormonal measurements, and ultrasonography of the ovaries. A control group of 24 ovulatory, nonhirsute, nonalopecia individuals was also studied. Of the 109 patients, 70 (64.2%) had no clinical evidence of hirsutism or menstrual dysfunction. Two of 44 patients tested with cosyntropin (Cortrosyn) had 21-hydroxylase deficiency, whereas two other patients had hyperprolactinemia caused by pituitary tumors. Hyperandrogenism was defined as an increase in any of the plasma androgens (testosterone, non-sex hormone-binding globulin bound testosterone, dehydroepiandrosterone sulfate, androstenedione, or dihydrotestosterone) and was noted in 42 of the 109 patients studied (38.5%). Of these 42 patients, 11 were ovulatory with no evidence of clinical hirsutism, 13 were ovulatory and hirsute, and 18 had oligomenorrhea or amenorrhea with or without hirsutism with confirmatory evidence of polycystic ovarian disease. Patients with diffuse alopecia may demonstrate hyperandrogenism, even in the absence of hirsutism, oligomenorrhea, or amenorrhea. The most common endocrine disorder in this series of patients with diffuse alopecia was polycystic ovarian disease.