Dementia with Lewy bodies (DLB) is the second most common form of dementia after Alzheimer disease (AD), accounting for up to 20% of all patients presenting with cognitive decline. The clinical diagnosis is made on the grounds of progressive dementia in the presence of fluctuating cognition, visual hallucinations, and extrapyramidal features (parkinsonism). The pathological hallmarks are neocortical Lewy bodies (LBs) with variable amounts of AD-related pathologic features (senile plaques and, to a lesser extent, neurofibrillary tangles). This article cites several seminal observations regarding the clinical presentation, nosologic history, and pathology of DLB.