A 65-year-old woman presented with a mild memory impairment, spatial disorientation, and poor task initiation. Progression was rapid over 3 months. She developed severe apathy, delusions, extrapyramidal features, and psychometrically quantified cognitive deterioration. Her brain showed many neocortical neuritic plaques and neurofibrillary tangles along with neocortical and brainstem Lewy bodies and temporal lobe spongiform vacuolization. This case is the most rapid deterioration documented of a patient with Alzheimer's disease and Lewy bodies.