Dementia with Lewy bodies is probably the second most frequent neurodegenerative dementia. Its neuropathological features overlap those of both Parkinson's disease and Alzheimer's disease, and the neuropathological hallmarks are therefore uncertain. Dementia with Lewy bodies is rather a clinical syndrome than a "neuropathological diagnosis". A combination of six original but non specific features is useful for diagnosis, namely fluctuating attention and cognition; recurrent daytime well-formed and detailed visual hallucinations; features of parkinsonism; rapid eye movement sleep behavior disorders; severe neuroleptic sensitivity; and low dopamine uptake in the basal ganglia. Because of the therapeutic implications, diagnosis of dementia with Lewy bodies is an important challenge.