In a series of 37 Parkinson's disease (PD) brains, cortical changes were reexamined by means of Bielschowsky silver impregnation and anti-ubiquitin immunocytochemistry. Compared to routine HE staining, anti-ubiquitin immunostaining revealed neocortical Lewy bodies (LBs) in a significantly higher percentage (76% vs. 32%). Neocortical senile plaques (SPs) occurred more frequently in brains with neocortical LBs than in cases without LBs (50% vs. 11%; p < 0.05). Semiquantitative assessment of neocortical LB density correlated with the frequency of occurrence and density of neocortical SPs. Dementia was confined to patients with abundant neocortical LBs, thus fulfilling histological criteria of diffuse Lewy body disease. We conclude that neocortical LBs are a very frequent feature of PD, although abundance of cortical LBs is confined only to a small subgroup with prominent dementia: diffuse Lewy body disease.