Senile plaques (SP) in the cerebellum of 23 cases of Alzheimer's disease (AD), three with widespread amyloid angiopathy, were studied with a modified Bielschowsky stain and immunocytochemical methods using antibodies to a beta-amyloid synthetic peptide (beta ASP), phosphorylated neurofilament proteins, ubiquitin, tau protein, and glial fibrillary acidic protein (GFAP). The four subtypes of SP (diffuse plaques, compact plaques, perivascular plaques, and subpial fibrillar deposits) that were observed with the modified Bielschowsky stain were also stained with antibodies to beta ASP. Many cerebellar SP contained ubiquitin-positive granular elements resembling dystrophic neurites. In contrast to neuritic elements in cerebral SP in AD, ubiquitin-positive elements in cerebellar SP were not labeled with antibodies to phosphorylated neurofilament or tau proteins. Various degrees of glial reaction were observed in all subtypes of SP except diffuse plaques. The absence of phosphorylated neurofilament and tau epitopes in neuritic elements in cerebellar SP is not surprising since paired helical filaments have not been seen in the cerebellum. Nevertheless, our results suggest that cerebellar SP are frequently associated with dystrophic neurites.