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 (p < 0.001 and 0.02, respectively). The 24-hr mean plasma cortisol concentration in 18 patients was 10.6 μ/dl and was significantly higher than that of the controls (6.8 μ/dl, p < 0.001). The average excretion of urinary free cortisol in nine patients was 205 μ/day, significantly greater than that of 65 μ/day in the controls (< 0.01). 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.