A review of human genetic mutations that affect aging and their potential contribution to help understand normal aging processes is presented. The lifespans of most animal species, including man, have a genetically determined maximum. The lifespan of man appears to have evolved exceedingly rapidly, which suggests that relatively few genes may determine longevity. Analysis of biochemical evolution suggests that the regulation of enzyme levels may underlie most evolutionary changes. There is a wide spectrum of human genetic mutations. Some, such as progeria and Werner's syndrome, produce a phenotype resembling premature aging and may involve genes related to the aging process. Certain human chromosomal abnormalities, such as Down's syndrome, produce an appearance of premature aging and may be due to abnormal gene regulatory mechanisms. Progress in understanding the genetic mechanisms underlying aging is likely to come from elucidation of the molecular defects that result in the premature aging syndromes and from insights gained regarding the regulatory mechanisms governing eukaryotic genetic expression.