Multiple myeloma (MM) can present with involvement of the central nervous system in the form of nerve palsy, plasma cell masses or, rarely, with endocrinological effects due to involvement of the pituitary gland. Usually, in such cases, the disease has a rapid progression and poor prognosis. We report a 52-year-old man who was admitted to the Kolkata Medical College, Kolkata, India, in 2016 with a prolonged low-grade fever and hypernatremia. Shortly afterwards, the patient began to complain of increased urinary frequency and drowsiness. The hypernatremia was treated with intranasal desmopressin and free water replacement. Serum protein electrophoresis and an immunofixation study revealed an immunoglobulin G-x monoclonal band. Magnetic resonance imaging of the pituitary gland revealed the absence of a posterior bright spot and spotty infiltration of the pituitary fassa. A bone marrow biopsy confirmed a diagnosis of cranial diabetes insipidus due to posterior pituitary MM infiltration.