Ageing and immunological function in man is considered in terms of morphological changes with age in central and peripheral lymphoid tissues and functional changes with age in humoral and cell mediated immune function. Thymic atrophy with ageing is emphasized and may be critical. Humoral immunity, particularly towards ubiquitous and complex bacterial antigens, is not demonstrably impaired, although there may be ‘spotty’ losses of reactivity (clonal failure) for infrequently encountered antigens of limited heterogeneity. T cell depletion with age is demonstrable by most methods of testing, cutaneous responses to ubiquitous antigens, sensitization by DNCB and responsiveness to mitogenic effects of PHA. Autoantibodies to nuclear and tissue specific antigens increase in prevalence with ageing. An immunoepidemiological study showed a correlation between autoantibodies and various indices of cardiovascular disease, and mortality was greater in subjects with autoantibodies.