An analysis of the growth patterns of 30 children with congenital adrenal hyperplasia (CAH) treated with cortisone acetate revealed 76% to be at or below the third percentile by age 2 years. Paradoxically, the growth rate was better in the first six months of life when the dose of cortisone per unit of body surface was highest. Among this group of 30 children, a sample of six children receiving therapy intramuscularly showed no significant difference in their growth hormone response to arginine hydrochloride or insulin stimulation when compared with a group of normal children. These data are consistent with an antagonism by cortisone of the actions of growth hormone at the peripheral level rather than a central inhibition of growth hormone release. In addition, linear growth in the first 6 months of life seems relatively independent of the growth suppressing effects of glucocorticoids.