We report a new case of Whipple's disease (WD) confined to the central nervous system. The patient presented with ataxia, ophthalmoplegia, hypersomnia, hemiparesis and generalized myorhythmia. The diagnosis was confirmed by identification of specific sequences of the causal agent of WD, the actinobacteria Tropheryma whippelii (TW), by PCR of DNA extracted from peripheral blood. An epidemiological survey of TW in patients with dementia suggests that WD is an uncommon cause of dementia in our population. Molecular methods may allow rapid identification of TW in peripheral fluids, and non-invasive diagnosis of this disorder.