Adrenocortical activity was studied in 19 emaciated women with anorexia nervosa. Relative to body size the patients' mean cortisol production rates of 0.591 mg/kg/day and 16.4 mg m2/day were significantly elevated compared to those of 0.322 mg/kg/day and 11.4 mg/m2/day for age and sex matched normal controls. The 24 hr mean plasma cortisol concentration in 18 patients was 10.6 μg/dl and was significantly higher than that of the controls (6.8 μg/dl). The average excretion of urinary free cortisol in nine patients was 205 μg/day, significantly greater than that of 65μg/day in the controls. Three patients underwent overnight suppression with 1 mg of dexamethasone and had inadequate responses. These data suggest that cortisol production is excessive in emaciated patients with anorexia nervosa due to a disturbance of the hypothalamic pituitary mechanisms regulating adrenocortical function. The excessive adrenal activity may reflect certain psychobiological disturbances as well as the effects of malnutrition.