BACKGROUND: The purpose of this study was to describe the associations between different levels of long-term physical activity in leisure time and subsequent causes of deaths. DESIGN: The Copenhagen City Heart Study is a prospective cardiovascular population study of 19 329 men and women aged 20-93 in 1976. Physical activity in leisure time was estimated at the examinations in 1976-78 and 1981-83. This analysis consists of 2136 healthy men and 2758 women aged 20-79 years, with unchanged physical activity at the two examinations, and with all covariates included in the multivariate analyses: smoking, total-cholesterol, high-density lipoprotein-cholesterol, systolic blood pressure, diabetes mellitus, alcohol consumption, body mass index, education, income, and forced expiratory volume in 10.78 (% predicted). RESULTS: Adjusted relative risks (95% confidence interval) for coronary heart disease were, for moderate physical activity 0.71 (0.51, 0.99) and for high 0.56 (0.38, 0.82). For cancer, moderate activity 0.77 (0.61, 0.97) and high activity 0.73 (0.56, 0.95) and for all-cause mortality, moderate 0.78 (0.68, 0.89) and high 0.75 (0.64, 0.87) for both sexes combined. Using Kaplan-Meier plots we calculated gained years of expected lifetime from age 50. Men with high physical activity survived 6.8 years longer, and men with moderate physical activity 4.9 years longer than sedentary men. For women the figures were 6.4 and 5.5 years, respectively. CONCLUSION: Long-term moderate or high physical activity was in both sexes associated with significantly lower mortality from coronary heart disease, cancer and all-causes. The same tendency was found for stroke and respiratory diseases, but the associations did not reach statistical significance.