A 74-year-old man developed fever, somnolence, hyponatremia, and life-threatening sinus bradycardia for three weeks. He showed a slight elevation of lymphocyte count and protein level in the cerebrospinal fluid. A brain CT scan revealed a diffuse low density area around the hypothalamus which was identified as a high intensity signal by flair MR imaging. Marked sinus bradycardia developed with no abnormality in the echocardiograph or cardiac enzymes. Over the next 6 weeks he became alert and normal sinus rhythm resumed. The results of endocrine tests were compatible with hypothalamic insufficiency with partial hypopituitarism and the syndrome of inappropriate secretion of ADH.