At post-mortem, Lewy bodies (LBs) were found in the brainstem and neocortex of eight out of 65 patients who had been collected during a prospective long-term study on clinically diagnosed Alzheimer's disease. All eight patients had accompanying Alzheimer pathology which was less severe than in a sample of eight age- and sex-matched patients from the same study with neuropathologically verified Alzheimer's disease. Parkinsonian features were more common in patients with LBs. There were no particular differences in duration of illness, severity of cognitive impairment, presence of hallucinations, or fluctuations in the course of illness. Frontal cerebral atrophy was more marked in patients with LBs, as was the loss of neurons in the basal nucleus of Meynert and the substantia nigra. Cognitive performance correlated with the number of pigmented neurons in the substantia nigra. We conclude that the differential diagnosis of LB dementia should be considered in patients satisfying NINCDS-ADRDA criteria for Alzheimer-type dementia who show marked Parkinsonian features and a frontal accentuation of cerebral atrophy.