A 63-year-old woman with Wernicke-Korsakoff syndrome, despite the absence of alcoholism and malnutrition, is reported. She had undergone gastrojejunostomy for ileus 30 years ago, and this operation was thought to be an important risk factor for her vitamin B1 deficiency. Brain MRI showed symmetrical high intensity areas on T2-weighted images in the periaqueductal region and bilateral dorsomedial nuclei of the thalamus. On single photon emission computed tomography (SPECT) using 99mTc-hexamethylpropyleneamine oxime, bilateral frontal perfusion was reduced, which was attributed to thalamo-cortical diaschisis due to injury to the dorsomedial nuclei of the thalamus. Presumably this phenomenon explains the Korsakoff psychosis. A history of gastrojejunostomy, even if normal intake is possible, is a risk factor for vitamin B1 deficiency, and should be considered in the differential diagnosis of Wernicke-Korsakoff syndrome.