Detailed neuroendocrine studies were carried out in a patient with histiocytosis X involving the hypothalamus. She presented with amenorrhea, galactorrhea, and diabetes insipidus. The diagnosis was established through needle biopsy with the aid of a computerized tomography (CT) scanner. The basic pathology and clinical features of the disease are outlined, with particular emphasis on the endocrine abnormalities seen in isolated hypothalamic histiocytosis X.