Dementia associated with cortical Lewy bodies on neuropathologic examination may comprise the second largest category of age-related cognitive impairment, after Alzheimer's disease. Despite its prevalence, a consensus has not yet been reached regarding the terminology, neuropathologic criteria, or clinical symptomatology of this postulated nosologic entity. Lewy body disease (LBD) is beginning to be diagnosed clinically in neuropsychiatric clinics, but universally accepted diagnostic criteria for LBD remain to be validated. In this article the authors review the literature on LBD, including both neuropathologic and clinical findings.