The Workshop on Epidemiologic and Public Health Aspects of Physical Activity and Exercise was conducted by the Centers for Disease Control on September 24-25, 1984. Fundamental topics were identified prior to the workshop, and experts were invited to participate. Ten papers were written, discussed at the workshop, revised, and are herewith published. The beneficial effects of physical activity on health are becoming progressively more apparent. A reduced risk of coronary heart disease, desirable weight control, and the reduction of symptoms of anxiety and mild to moderate depression are established. Beneficial effects on hypertension, type II diabetes, osteoporosis, and certain psychiatric and psychologic conditions appear likely but require additional study. Although the importance of physical activity to health is becoming better established, several important gaps in our knowledge remain. Physical activity is a complex behavior that is difficult to measure, and the accuracy of most measurement instruments is not known. Knowledge of the patterns of physical activity within our society and the determinants of those patterns is limited. Information on the rates of mechanical, metabolic, and psychologic risks of physical activity is largely absent. In addition, there is a need to know more about the dose-response effects of physical activity, the differential effects on various subgroups of the population, the specific dimensions of activity which effect different aspects of health, and the efficacy of various intervention and promotional strategies. Each paper stands as an independent contribution to the literature. As a group, the authors of these papers have provided the public health and scientific communities with a succinct yet comprehensive summary of the status of knowledge plus specific recommendations for future research in the areas of physical activity, public health, and epidemiology.