A case of an elderly man who developed severe hyponatremia and bone marrow granulomatosis while taking methyldopa is described. The hyponatremia was found to be due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Bone marrow biopsy revealed granulomas. A MEDLINE search of the English literature was done, yielding only one previous report of methyldopa-induced bone marrow granulomatosis and no previous reports of methyldopa-induced SIADH.