Natural killer (NK) cells are a key component of innate immunity involved not only in the elimination of virus-infected or tumor cells but also in the regulation of the immune response by producing cytokines and chemokines that can activate other cellular components of innate and adaptive immunity. NK cell subsets are differentially affected by aging. Whereas CD56(bright) cells are decreased in healthy elderly individuals, the CD56(dim) subset is expanded. The expression of CD57, a marker of highly differentiated NK cells, is increased in the elderly; this supports the notion that a remodeling process of NK cell subsets occurs in aging with a gradual decrease in more immature CD56(bright) NK cells and an increase in highly differentiated CD56(dim) CD57+ NK cells. This NK cell redistribution can explain many of the phenotypic and functional changes in NK cells associated with healthy aging such as decreased proliferation and the maintenance of CD16-dependent cytotoxicity.