Background. Hypophysitis is an inflammatory disease of the pituitary gland that may mimic pituitary tumors clinically and radiologically. Case Description. We report a case of a xanthomatous hypophysitis initially diagnosed as pituitary adenoma. A 31-year-old woman presented with headache, diabetes insipidus, and amenorrhea. A head CT scan showed no intrasellar changes, while an MRI scan showed a sellar cystic mass. An endocrinological work up revealed mild hypocortisolism and diabetes insipidus (DI). Transsphenoidal surgery was performed. The intraoperative histological examination suggested a pituitary adenoma. The removed tissue showed central necrosis surrounded by accumulation of foamy cells and xanthomatous epithelioid cells. The patient made an uneventful postoperative recovery, Nevertheless, DI persisted and the adenohypophysis hypofunction did not recover. Conclusion. We describe an unusual inflammatory lesion of the pituitary gland mimicking an adenoma. A high level of clinical suspicion of inflammatory disorders is necessary for correct diagnosis and optimal management.