A patient with encephalopathy developed triphasic changes in the clinical course, starting with diabetes insipidus (DI), then the syndrome of inappropriate ADH secretion (SIADH), and followed by the final phase of DI. The clinical course of encephalopathy was very rapid. The patient lost consciousness completely within only one day after the onset. During the early phase, he lapsed into a condition of "brain death". We could not identify the etiology of the encephalopathy. The triphasic change referred to above is similar to previous reports of cats model after stereotactic destruction of the supraopticohypophyseal tract. We speculate that our case may have been associated with neurohypophyseal dysfunction caused by supraopticohypophyseal tract damage.