Dysregulated immunity, 'immunosenescence', in the elderly is thought to contribute to their increased susceptibility to infectious disease and to impact on mortality. Accepted hallmarks of human immunosenescence are low numbers and frequencies of naïve T cells and higher numbers and frequencies of memory T cells in the peripheral blood of the elderly compared to the young. The proportion of the population infected with CMV increases with age and markedly influences these parameters. Infection with this persistent β-herpesvirus may therefore indirectly impact on survival in the elderly. Recent evidence pertaining to this controversial proposal is reviewed here.