Dementia with Lewy bodies (DLB) is the second most frequent cause of primary degenerative dementias, following Alzheimer's disease (AD). The nosologic situation of this disease has fragile limits. There is controversy as to whether Parkinson's disease (PD) and DLB are two different entities or whether they make up part of the same spectrum. The terms diffuse Lewy bodies disease and the variant of Lewy bodies in senile dementia or AD have been used to describe pathologic changes with clinical manifestations of dementia and parkinsonism. At present, DLB should be understood as an entity with the essential feature being the presence of Lewy bodies in the brain stem and cerebral cortex. From the point of view of clinical examination, DLB is characterized by the presence of subcortical or progressive cortical dementia, at times without severe memory disorders, with great fluctuations and well detailed recurrent visual hallucinations. These cognitive alterations are associated with parkinsonism. Other frequent disorders are falls, syncopes, transitory alterations in consciousness, great sensitivity to neuroleptic drugs and visual illusions with pseudoperception. The correct diagnosis of this entity is important to administer adequate treatment, to avoid classical neuroleptic drugs and to establish precise prognosis. From a therapeutic point of view, cholinesterase inhibitors show some efficacy in the treatment of cognitive alterations.