Forty two women with hidradenitis suppurativa were assessed clinically and biochemically for evidence of androgen excess. Thirteen had irregular menses; 22 of 36 experienced exacerbation of hidradenitis suppurativa premenstrually; 19 had or had had acne vulgaris; and seven were hirsute. Comedones (blackheads) were found in apocrine sites in 37, but also in retroauricular sites in 18 and were considered to be an important physical sign for early diagnosis. Eight had evidence of pilonidal (postanal) sinus. The patients had a higher concentration of total testosterone (p less than 0.01) and free androgen index (testosterone to sex hormone binding globulin concentrations) (p less than 0.01) than normal controls. Patients with hidradenitis suppurativa appear to have endocrine abnormalities sufficient to suggest an androgenic basis for the disease.