A 45-year-old female presented with blurred vision, headache, and abnormal thirstiness. She was not pregnant nor postpartum. She had diabetes insipidus and bitemporal hemianopsia. Radiological evidence suggested a mass arising in the sella turcica with extension into the parasellar and suprasellar regions. Carotid angiography showed occlusions of bilateral internal carotid arteries at the cavernous portions. The mass was subtotally removed by the trans-sphenoidal approach and was histologically diagnosed as an adenohypophysitis. Laboratory data showed the patient to be in an active state of autoimmune disorder and hypopituitarism. When a patient presents with pituitary insufficiency and an enhanced intrasellar mass lesion on computed tomographic scan, lymphocytic adenohypophysitis must be included in the differential diagnosis.