Dementia with Lewy bodies appears to be the second most common form of dementia, accounting for about one in five cases. The condition is characterized by dementia accompanied by delirium, visual hallucinations, and parkinsonism. Other common symptoms include syncope, falls, sleep disorders, and depression. The presence of both Lewy bodies and amyloidplaques with deficiencies in both acetylcholine and dopamine neurotransmitters suggests that dementia with Lewy bodies represents the middle of a disease spectrum ranging from Alzheimer's disease to Parkinson's disease. The diagnosis of dementia with Lewy bodies is based on clinical features and exclusion of other diagnoses. Individualized behavioral, environmental, and pharmacologic therapies are used to alleviate symptoms and support patients and their families. Cholinesterase inhibitors are more effective in patients who have dementia with Lewy bodies than in those with Alzheimer's disease. Conversely, patients who have dementia with Lewy bodies do not respond as well to antiparkinsonian medications. Anticholinergic medications should be avoided because they exacerbate the symptoms of dementia. Traditional antipsychotic medications can precipitate severe reactions and may double or triple the rate of mortality in patients who have dementia with Lewy bodies.