In a consecutive series of 30 brains of demented patients (presenile, senile and familial types) with the histological hallmarks of Alzheimer's disease, cerebellar amyloid plaques and cerebellar amyloid angiopathy were observed in 80% of the cases. These cerebellar amyloid plaques were sometimes centered on a small amyloidotic blood vessel. They were immunostained with A4 antiserum, but they were not surrounded by a crown of swollen neurites as demonstrated with silver impregnation and Tau antiserum. They were not immunostained with SAF antiserum which decorated the cerebellar Kuru-like plaques observed in subacute transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker syndrome. The absence of neuritic changes around the numerous cerebellar amyloid plaques frequently observed in cases of Alzheimer's disease is an interesting feature and will perhaps explain the mechanism of cytoskeleton changes occurring in the neurons of the cerebral cortex.