To assess the value of promoting health through exercise, we review what is known about the medical and medical care resource costs and benefits of exercise. Literature searches were undertaken to derive estimates of the relative risk, in individuals who exercise regularly compared with those who do not, of each of the major disease groups for which there is good evidence that the disease can be ameliorated by exercise (coronary heart disease, stroke, diabetes, hip fracture, and mental illness). These relative risks were used to estimate the incidence of hospital admissions and mortality, and associated healthcare costs, which could be prevented if the whole population exercised. Literature on the incidence and costs of exercise-related morbidity and mortality was also reviewed to derive estimates of both the costs to health and also the healthcare resource implications of exercise in total population. Indirect costs and benefits, and also quality-of-life effects associated with exercise were not included in this assessment. The results show that in younger adults (ages 15 to 44 years) the average annual medical care costs per person that might be incurred as a result of full participation in sport and exercise (approximately 30 pounds British sterling) exceed the costs that might be avoided by the disease-prevention effects of exercise ( less than 5 pounds British sterling per person). However, in older adults ( greater than or equal to 45) the estimated costs avoided ( greater than 30 pounds British sterling per person) greatly outweigh the costs that would be incurred ( less than 10 pounds British sterling). There was little evidence that exercise leads to deferred health or health service resource benefits. We conclude that with regard to health and medical care costs, there are strong economic arguments in favour of exercise in adults aged greater than or equal to 45 but not in younger adults. Estimates derived from the international scientific literature and routine UK data sources may have limited direct application in the healthcare systems of other countries. Nevertheless, the result that exercise costs exceed the benefits in younger adults but vice versa in older people is likely to be generally true. Indeed, a similar result has been found in a study of a Dutch population.