Cytomegalovirus (CMV) infection exerts an enormous effect on human immunity, as it is associated with an immune-impaired response, a variety of chronic diseases, and overall survival in elderly individuals. Levels of anti-CMV antibodies may be associated with the differentiation degree of T cell subsets. Titers are significantly higher in the elderly and positively correlated with specific CD4(+) T cell responses to CMV. In the elderly, antibody titers are associated with the degree of differentiation and the T cell receptor excision circle (TREC) content in CD4(+) T cells, with other features of the immune risk profile, and with a reduced ability to respond to immunization in vivo. Associations may be absent in young subjects because their anti-CMV antibody titers are lower than those of the elderly. However, comparing young and elderly individuals with similar antibody levels reveals differences in their highly differentiated and naïve T cells. These are more marked in individuals with high titers. In parallel with the increase in anti-CMV antibodies, the elderly experience a significant reduction in absolute counts of naïve CD4(+) T cells, which may be a strategy to compensate for the expansion of differentiated cells and to avoid an increase in total T cells. In summary, our results show that titers of anti-CMV antibodies, and not only CMV seropositivity, are related to differentiation status and immunocompetence in the elderly, making this as an important prognostic marker of the status of immune system function.