Cytomegalovirus infection is very common and leads to the generation of a very strong humoral and cellular immune response that is maintained for life and appears necessary to control viral replication. This leads to marked alterations in the composition of the immune cell repertoire and epidemiological evidence shows that this can be associated with increased levels of morbidity and mortality in the elderly. The immune response appears to be triggered by frequent episodes of subclinical viral reactivation and the predominant effect is of the accumulation of large numbers of cytotoxic cells. These observations suggest that mechanisms that could serve to control the expansion of this immune response could have significant potential in improving the health of elderly donors.