Premortem diagnosis of diffuse Lewy body disease (DLBD) is difficult, and knowledge of the parkinsonian features of DLBD might facilitate the diagnosis. In this study, we compared the parkinsonian syndrome of DLBD and Parkinson's disease (PD). We retrospectively reviewed the charts of Columbia-Presbyterian Medical Center (CPMC) Brain Bank cases (1989-1993) with pathologically diagnosed DLBD or PD, and the literature on the parkinsonian features in DLBD patients presenting with parkinsonism. Parkinsonism accompanied or preceded cognitive/psychiatric changes in most CPMC cases (DLBD 100%, PD 88%). DLBD had an earlier mean age of onset than PD did (57 versus 64 years), a similar male:female ratio (1.7:1 versus 1.9:1), and similar mean disease duration (12-13 years). Cognitive/psychiatric changes were less frequent in PD than in DLBD (65 versus 100%) (p = 0.025). Rest tremor was specifically mentioned in 29% of DLBD versus 56% of PD (p = 0.10). Bradykinesia was less common in PD (56% versus 86%) (p = 0.05). All those with PD responded to L-Dopa, as did all those with DLBD who received L-Dopa. In conclusion, there are subtle differences between PD and DLBD in age of onset, frequency of cognitive/psychiatric changes, bradykinesia, and rest tremor. However, even when taken together, these cannot be used to distinguish these entities.