Whipple's disease is infrequently considered in the differential diagnosis of patients presenting with progressive neurological deterioration. This is in part a result of the relative rarity of this entity and in part due to the more frequent initial presentation of the disease with gastrointestinal, musculoskeletal, or cardiovascular symptoms. A case is described in which the neurological symptoms of progressive dementia and weakness were seen in the relative absence of non-neurological symptomatology. The diagnosis of Whipple's disease was made from a brain biopsy. The neuropathology of Whipple's disease of the central nervous system is described and the importance of considering it as a treatable entity in the differential diagnosis of progressive neurological deterioration, despite the absence of systemic symptomatology, is stressed.