The adreno-genital syndrome (congenital adrenal hyperplasia) is caused by deficiency of an enzyme (usually C-21 hydroxylase) necessary for adrenal production of cortisol, which results in excessive accumulation of androgenic precursors. It is the most common cause of female pseudohermaphroditism. There have been a few sporadic reports of ultrasonic demonstration of enlarged adrenals in the adreno-genital syndrome. To determine whether ultrasonography could be used to establish or exclude the diagnosis, ultrasonic examinations were performed on eight newborn infants with ambiguous genitalia who were subsequently proven to have the adreno-genital syndrome. The adrenals were found to be enlarged in three patients, at the upper limit of normal in three patients, and in two infants the adrenals were well within normal limits in size. The uterus was identified in seven of the eight patients, but was not seen for technical reasons in one. It is concluded that ultrasound is useful in the evaluation of infants with congenital adrenal hyperplasia to establish the presence of a uterus and to demonstrate enlargement of the adrenals, but it should be cautioned that finding adrenals of normal size does not exclude the diagnosis. Key words ultrasound, adreno-genital syndrome, congenital adrenal hyperplasia.