A 37-year-old woman presented with acute psychosis and cognitive impairment. Skull x-ray showed an enlarged sella turcica with erosion of the floor. Endocrinologic workup suggested the diagnosis of Cushing's disease and hyperprolactinemia. She had no cushingoid feature, and the only physical sign was mild generalized obesity. She showed a paradoxic response to dexamethasone suppression, and underwent trans-sphenoidal resection of a pituitary macroadenoma. Electron microscopy showed the tumor to be a Crooke's cell adenoma. Results of immunohistochemical staining were positive only for ACTH and beta-endorphin. The neuropsychiatric manifestations resolved after surgery.