The discovery of widely distributed Lewy bodies (LBs) in the brains of patients with dementia has stimulated much clinical and pathologic inquiry. This clinico-pathologic syndrome is now referred to as dementia with Lewy bodies (DLB). Diagnostic criteria for DLB proposed at a workshop in 1995 are receiving detailed scrutiny. The criteria are complex to apply, and appear to have high specificity, but variable sensitivity. Neuropathologic studies have been aided by the development of probes against alpha-synuclein, a key component of LBs. Widespread LBs in limbic or cortical areas contribute to dementia. Pharmacologic management of cognitive and behavioral symptoms in patients with DLB is being explored. There is evidence that cholinesterase inhibitors may have beneficial effects.