We present a 22-year follow-up of a large and unusual kindred previously reported as familial Alzheimer's disease (FAD). However, detailed clinical and neuropathologic evaluation of family members and brain autopsy on another affected individual now make the diagnosis of FAD unlikely. Our patient, as well as members of this family, had numerous amyloid plaques and rare neurofibrillary tangles. These plaques were quite atypical for Alzheimer's disease (AD); many were quite large (up to 500 microns in diameter) and contained several amyloid cores, some with neuritic components. The plaques were present throughout the cerebral cortex and striatum, but not in the cerebellum. By electron microscopy, they had radiating star-shaped amyloid cores containing 8- to 10-nm fibrils, and a few dystrophic neurites. They were strongly immunoreactive with antiserum to prion protein but did not react with the antiserum to the amyloid A4 protein of AD. Although the cerebellum was uninvolved, this family appears to represent another clinical and neuropathologic variant of Gerstmann-Sträussler syndrome.