In a study of 102 women (Arabs and Asians) with hirsutism, polycystic ovary syndrome was diagnosed in 93 patients (91%) including 26 cases with hirsutism and regular menstrual periods. In more than half of the cases the diagnosis was made on the basis of transabdominal ultrasonography, which was the single test with the highest yield. Luteinising hormone hyperresponsiveness to gonadotropin-releasing hormone was positive in only seven of 50 patients tested. Late onset congenital adrenal hyperplasia due to 21-hydroxylase deficiency was identified in two cases, thus forming a prevalence of 8% in those who underwent adrenocorticotropin stimulation. In one case, polycystic ovary syndrome was an associated condition. In this study of a population of women with hirsutism and regular menses, the majority had polycystic ovaries. It is suggested that the term 'idiopathic or racial' hirsutism should not be applied unless a thorough evaluation has failed to reveal a diagnosable underlying disorder.