A 70-year-old man with a 28-year history of type 2 diabetes mellitus was admitted due to persistent vomiting and neurological abnormalities in Nov 2012. He had developed gait disturbance and diplopia for six months during antiplatelet therapy, which was initiated following the diagnosis of a cerebellar infarction in June 2012. He had nystagmus, truncal ataxia and an ocular motility disorder, and the MRI study showed increased FLAIR and DWI signals in the peri-third ventricle and periaqueductal region, in addition to the cerebellar vermis. Wernicke encephalopathy was suspected according to his symptoms, and thiamine administration dramatically improved his condition. He did not have a history of alcohol abuse or poor eating habits; however, various coexisting factors, including diabetes mellitus, pyloric stenosis and the use of antiulcer drugs and insulin, were considered to be responsible for Wernicke encephalopathy. This case demonstrates the importance of distinguishing Wernicke encephalopathy from cerebrovascular disease in elderly patients.