Aging is a complex phenomenon involving multiple physiological functions. Among these, very important are the modifications induced in the immune system; these modifications may be related to cancer development, a disease of older people. We herein describe the age-dependent alterations observed in the various arms of the immune system. Both innate and adaptive immunity are compromised during aging, a condition where an inflammatory status contributes to promote immune suppression and tumour growth. Collectively, aging of the immune system may produce detrimental consequences on the response against tumours in old patients. In fact, preclinical studies and clinical observations in humans have demonstrated age-associated alterations in antitumor immunity. Immunological recovery of old patients after conventional chemotherapy (CT) has not been fully investigated, while several studies conducted in patients undergoing blood stem cell transplantation have demonstrated that a delayed immune reconstitution associated with older age results in increased susceptibility to opportunistic infections and risk of tumour relapse. Cellular immunotherapy and vaccination are becoming viable options for improving survival and quality of life of cancer patients targeting both the host defences and the tumour. The clinical experience in elderly patients is still in its infancy, but available data indicate that these approaches are feasible and promising. A key problem in the studies on aging, immunity and cancer is that it is difficult to distinguish changes related to age from those related to cancer-dependent immunosuppression, but independent from the age of the subject. Longitudinal studies on aged healthy and cancer persons and the use of new immunological techniques may be required to clarify these issues.