Seventy-seven female patients (36 adults and 41 children aged under 16 years) with congenital adrenal hyperplasia (CAH) were assessed using pelvic ultrasound, as well as with standard endocrine tests and HLA typing. Forty-six close female relatives were also tested for ovarian morphology using ultrasound after assessment of their heterozygous state using HLA typing. The association of CAH with ultrasonically detected polycystic ovaries (PCO) was confirmed in 30/36 (83%) adult patients, 4/10 (40%) postpubertal girls and 1/31 (3%) pre and peripubertal girls: in all, 35/46 (76%) postmenarcheal patients. Six out of nine (67%) pre-menopausal mothers of patients with PCO, and 8/10 (80%) sisters of patients with PCO also had PCO. The proportions of both CAH patients and heterozygote subjects with PCO were significantly greater than that found in a normal population (P less than 0.0001). The finding, however, of two homozygous non-CAH-affected adult sisters with PCO and, conversely, of 10 heterozygous adult relatives and of 12 postmenarcheal CAH patients with normal ovaries, indicates that the ovarian morphological change may be independent of the adrenal lesion.