This brief review examines the likelihood that a deterioration of aerobic fitness will lead to a loss of independence in old age. The rate of deterioration of maximal aerobic power observed in middle-aged adults continues unabated during the retirement years. Loss of independence seems likely if maximal oxygen intake falls below a threshold of 18 ml/[kg.min] in men, and 15 ml/[kg.min] in women, reached at 80-85 years. A regular programme of aerobic exercise can slow or reverse the functional deterioration, reducing the individual’s biological age by 10 or more years, and potentially postponing dependency by a similar amount. There remains a need to clarify the importance of decreasing aerobic fitness relative to other potential causes of dependency, but from the practical viewpoint regular aerobic activity should be commended to seniors, since it can address many of the issues of both functional loss and chronic disease.