Thirty-seven Japanese autopsy cases with diffuse Lewy body disease (DLBD) were reviewed from a clinicopathological viewpoint. Based on the neuropathological finding of whether or not many concomitant senile plaques (SPs) and/or neurofibrillary tangles (NFTs) are present. DLBD is divided into two forms: a common form and a pure form. In the common form not only numerous Lewy bodies but also many SPs and/or NFTs are found in the cerebral cortex, whereas in the pure form there are no or few senile changes. Of the 37 cases, 28 cases had the common form, and 9 had the pure form of DLBD. In the common form all cases had shown progressive cortical dementia in the presenile or senile period. About 60% of the cases began with memory disturbance, while 25% showed Parkinson's or Shy-Drager syndrome initially. Parkinson's syndrome, consisting mainly of muscular rigidity and akinesia, was usually marked in the later stage, although there were also 8 cases (28.6%) in which no parkinsonian symptoms were detected even in the terminal stage. On the other hand, almost all cases with the pure form of DLBD showed juvenile Parkinson's syndrome, followed by progressive cortical dementia, although there was one presenile case with mild dementia and Parkinson's syndrome. These Japanese cases are compared with cases reported in Western countries.