Scientific progress in human immunosenescence research is pointing increasingly towards the clinical importance of age-associated changes in immunity, although many areas remain controversial. For infectious disease, there is accumulating good empirical evidence, discussed in this review, that immunosenescence compromises protection in elderly people. This implies that an age-associated decreasing immunity results in increased incidence of those diseases that the immune system is designed to protect against, i.e. infectious diseases. This unsurprising conclusion suggests that preventing these infections using interventions designed to prevent or reverse immunosenescence could extend the period of life enjoyed in good health.