To study the pathophysiology of hypercortisolism in anorexia nervosa, we measured the cerebrospinal fluid (CSF) levels of corticotropin-releasing hormone (CRH) in patients when they were underweight and at intervals after weight restoration. CSF CRH levels were significantly elevated in hypercortisolemic underweight patients. Both CSF CRH levels and pituitary-adrenal function normalized after weight recovery. A significant positive correlation was found between CSF CRH levels and depression ratings in weight-corrected patients. We conclude that the hypercortisolism of anorexia nervosa reflects a defect at or above the hypothalamus which results in the hypersecretion of endogenous CRH. The positive correlation between CSF CRH and depression in the weight-restored patients is compatible with previous data indicating increased CRH secretion in the depressed phase of primary affective disorder and supports the notion of a relationship between CRH and depressive symptomatology. Moreover, these data are compatible with observations that depression is part of the anorexia nervosa syndrome.