&NA;A cyclic excess of cortisol secretion was detected in a patient with diabetes insipidus and diabetes mellitus. The cycles of hypercortisolism were of 7 days' duration, but during the nadir of these cycles urinary excretion of corticosteroids and 17‐ketosteroids was within the normal range. The radiological appearance of the sella turcica was normal; however, computerized axial tomography of the head revealed a small tumor immediately superior to the sella turcica. At operation a small chromophobe adenoma superior to the diaphragma sellae and involving the hypophysial stalk was partially resected. Postoperatively, the patient continued to have 7‐day cycles of increased corticosteroid excretion, but the amounts excreted were less than they had been preoperatively. Other patients have been described in whom Cushing's disease has been due to cyclic hypercortisolism. These cycles have been remarkably regular in individual patients, but of variable duration in different patients. Furthermore, cyclic hormonogenesis probably occurs in a variety of endocrinopathies. (Neurosurgery,5: 598‐603, 1979)