A significant component of the aging process is genetically determined. Numerous theories of aging exist, many of which postulate the existence of "longevity genes". Recent advances in molecular biological and other techinques have allowed a significantly greater understanding of aging and age-related disease. This will be illustrated by four genetic and sporadic diseases: Alzheimer's disease (AD) and related disorders, transthyretin dementia, cerebral amyloid angiopathy-Icelandic type and scrapie related diseases. Alzheimer's disease (AD), the most common of this group, is the leading cause of dementia in Western countries. Recent genetic and biochemical studies have shown in involvement of at least four genes in the pathogenesis of AD. In early-onset familial AD mutations in the (beta)PP, S182 (presenilin 1) and STM2 (presenilin 2 or E5-1) genes have been found, while in the more common late-onset AD the presence of the apolipoprotein E4 isotype is a major risk factor. Genetic studies have also helped to elucidate the etiology of rarer cerebral amyloidoses such as the recently described Hungarian amyloidosis that is characterized by meningocerebrovascular amyloid deposition, with resultant dementia. This disease is linked to a mutation in the transthyretin gene. It is hoped that in the near future this increase in knowledge will allow the development of therapeutic approaches to slow the aging process.