Recent studies have shown a genetic association of the apolipoprotein E (ApoE) epsilon 4 allele with late onset familial and sporadic Alzheimer's disease (AD). In this study we analysed the possible association of the genetic polymorphism of the ApoE gene with age of onset in Italian familial Alzheimer's disease (FAD) families including two early onset familial Alzheimer's (EOFAD) families with the APP717 Val-->Ile mutation in the amyloid precursor protein (APP) gene on chromosome 21. In none of the FAD families analysed was there a significant effect of the ApoE genotype on the age of onset with the exception of one of the two mutated EOFAD families in which the epsilon 2 allele delayed the age of onset.