Rapid, accurate diagnosis of congenital adrenal hyperplasia (CAH) is essential in the neonate with ambiguous genitalia, life-threatening salt loss, or both. We aimed to determine the accuracy of adrenal ultrasonography in the diagnosis of CAH in a retrospective analysis of 52 children with ambiguous genitalia or salt-losing crises. Adrenal ultrasounds were interpreted as follows: "normal" if the adrenals were normal in size (adrenal limb width <4 mm), had a smooth surface, and a central echogenic stripe with a hypoechoic rim, and "abnormal" if they were increased in size (limb width >4 mm), had a lobulated or cerebriform surface, or showed abnormal echogenicity. Group 1 consisted of 25 neonates and infants with CAH; group 2, 19 children with conditions other than CAH; and group 3, 8 with treated CAH: 7 receiving replacement therapy and 1 whose mother received glucocorticoids during pregnancy. In all children in groups 2 and 3, adrenal ultrasounds were read as normal. In group 1 adrenal ultrasonography was normal in 2 (8%) and abnormal in 23 (92%). Thus adrenal ultrasonography has a sensitivity of 92% and a specificity of 100% for diagnosing CAH. Adrenal ultrasonography is a highly sensitive and specific adjunct in the diagnosis of CAH. The presence of enlarged, lobulated adrenals with stippled echogenicity is invariably associated with CAH.