In order to support the concept that a lesion of the thalamus is sufficient to cause a Korsakoff syndrome, we are presenting 5 patients, all of whom developed the syndrome after sustaining a left (dominant) thalamic infarction. Two patients had pure thalamic strokes followed by a permanent Korsakoff syndrome. One of these patients was studied with neuropsychometric testing, as well as with a modern MRI scan. In 2 other patients, clinical and imaging data indicate that infarction was not limited to the thalamus. Another patient had bilateral thalamic infarcts but only a temporary Korsakoff syndrome. Neuropathological data are needed to elucidate the exact anatomical substrate of dominant thalamic Korsakoff syndrome.