Four children with pituitary Cushing's syndrome are described. Growth velocity was retarded in all patients but, following adrenalectomy, returned to normal or "catch-up" rates. In two adolescent boys, testicular enlargement and virilization progressed prior to adrenalectomy, while their growth rates remained subnormal. Plasma growth hormone responses were subnormal in only one of the patients preoperatively. This 15-year-old boy had hyperadrenocorticism of the longest duration (eight years) but had the lowest glucocorticoid levels. Earlier in the course of his disease his growth hormone response to insulin had been normal. The study indicates that the primary cause of growth retardation in children with Cushing's syndrome is suppression of the end organ response to growth hormone. Attenuation of growth hormone secretion is a late and less frequent occurrence. Glucocorticoid excess also inhibits the growth promoting effect of androgenic hormones but does not inhibit virilization.