It has been well established that high fever can cause substantial damage to the cerebellum and also cause multiple small vascular lesions in neocortex and subcortical white matter. Beyond acute effects, the neuropsychological sequelae of these latter cortical and subcortical lesions have not been studied. The investigation reported involved 36 VA patients with a history of serious febrile illness. The febrile illnesses of the pyrexic subjects did not cause febrile seizures and resulted from diseases that did not directly involve the brain (e.g., encephalitis, meningitis, malaria). Control subjects were combat veterans who had suffered gunshot wounds, but who had no history of febrile illness. Pyrexic patients performed worse than controls on a variety of measures including language, memory, concentration, and word finding as well as failing a test of dichotic listening for words. Results demonstrate that hyperpyrexia can have lasting neuropsychological sequelae, and suggest that history of serious febrile illness be considered as an exclusionary criterion for participation in neuropsychological research concerning other topics or disorders.