Dementia with Lewy bodies (DLB) may be the cause of up to 20% of all dementias, giving way in frequency of causes only to Alzheimer's disease. The most typical symptoms of DLB are Parkinsonism, function of the cognitive functions and visual hallucinations. This clinical picture is often taken for "senile psychosis" (which encompasses cases of both acute and sub-acute hallucinatory and delusive syndromes with dementia and periodic disturbances of consciousness), an umbrella term probably concealing most undiagnosed cases of DLB. It is important from the clinical point of view that DLB be correctly diagnosed as a separate nosological unit and differentiated from Alzheimer's disease and dementia because DLB should be treated differently (it responds well to cholinesterase inhibitors and is hypersensitive to neuroleptics). The authors discuss the clinical picture, pathogenesis, differential diagnosis of DLB as well as current therapeutic indications.