We report a case of central diabetes insipidus (CDI) in a patient with AIDS due to cytomegalovirus (CMV) infection of the vasopressin-producing areas of the hypothalamus. The clinical diagnosis is established by definitive clinical and laboratory evidence of CDI. Detailed histopathological and immunohistochemical studies establish CMV as the causative agent and demonstrate the deficit of vasopressin in the synthesizing neurons. Physicians caring for patients with AIDS should be aware of CDI and adipsic hypernatremia as potential complications of CMV infection. The case also demonstrates that patients with diabetes insipidus do not have polyuria when glucocorticoid deficiency coexists.