Poor physical function and low muscle strength are significant predictors of mortality in rheumatoid arthritis, other chronic diseases, ageing individuals, and the general population. Poor physical function predicts earlier mortality in diseased and normal populations at levels of significance similar to or greater than most known biomedical predictors such as laboratory tests. This chapter summarizes data concerning the prediction of premature mortality by poor physical fitness and musculoskeletal function, according to performance and self-report measures. The data support recommendations for regular exercise in all individuals whether or not they have a disease, to promote health and longevity.