This is the first report of acute Wernicke's encephalopathy in which characteristic magnetic resonance (MR) findings have been verified by postmortem histopathological examination. The high-signal areas surrounding the third and the fourth ventricles and the aqueduct on the T2-weighted images reflected the spongy disintegration of the neuropil, which is the typical pathological finding in Wernicke's encephalopathy. We confirmed that MR imaging is essential to the early diagnosis of Wernicke's encephalopathy.