The immune system changes during the lifespan of man. Many described changes in the immune system of the elderly were dependent on illness or chronic diseases. To exclude these pathological changes in the immune system and to exclusively describe age-dependent changes, Ligthart et al. defined immunogerontological criteria to study the immune system in the elderly, the SENIEUR-Protocol. Most changes in the immune system of elderly are within the normal ranges of the appropriate parameter. However, there are many significant differences between the status of the immune system in healthy young and elderly individuals, within these normal ranges. The comparison between SENIEUR-elderly and healthy young and the additional comparison of these two groups with centenarians allows the discussion of potential pathological effects of these changes. In this article we summarize the described changes of the immune system in SENIEUR-elderly and centenarians. The serum levels of the immunoglobulins G, M and A increased with age, as well as the number of benign monoclonal gammopathies and the number of autoantibodies. The titers of zinc are significantly decreased in the serum of the elderly. The production of the acute phase protein C-reactive protein is not age-dependent, whereas the serum levels of alpha 2-macroglobulin are significantly increased in the elderly. The number of lymphocytes decreased and the number of neutrophils increased with aging. Monocytes, basophils, and eosinophils are without changes during life. There are many descriptions about changes of the leukocyte sub-population in aging, which are not always comparable. However, the number of T cells (CD3) decreases. Within the T cells the CD8 cells decreased more than the CD4 cells, resulting in an increased CD4/CD8 ratio. Memory T cells (CD45RO) increase during life, whereas naive T cells (CD45RA) decrease. Interestingly, centenarians have more naive T cells SENIEUR-elderly. The number of B cells (CD19) decreased also, whereas the number of natural killer (NK) cells (CD16, CD56, CD57) increases with aging. The capacity of leukocytes from the elderly to produce cytokines is also significantly different from those of the young. The release of the TH1-cytokines interleukin (IL)-2 and interferon (IFN)-gamma is decreased, whereas the production of the TH2-cytokines IL-4 and IL-10 is increased in the elderly. The production of proinflammatory cytokines such as IL-1, IL-6, IL-8, and tumor necrosis factor-alpha is increased in the elderly. In contrast, the capacity to produce the antiviral cytokine IFN-alpha is reduced in elderly individuals. In conclusion, the immune system shows many age-dependent changes, but we know little about the reason and the potential pathological effects of these changes.