Diffuse Lewy body disease is the second cause of dementia after Alzheimer's disease. It is characterized by a progressive dementia, often difficult to differentiate from Alzheimer's disease, but fluctuations of cognitive deficits, frequent hallucinations, delirium, hypersensitivity to neuroleptics, unexplained falls, atypical receiving "black-outs" and parkinsonian features are characteristics features evocative of the diagnosis. The response to anticholinesterase medication is often much better than in Alzheimer's disease.