Diabetes mellitus is a common chronic disorder the primary therapeutic principles of which have long been based on the combination of physical activity with appropriate diet. Although exercise in insulin-dependent diabetes mellitus (IDDM) may be associated with metabolic deterioration in the case of lack of adequate provision of insulin and carbohydrate in balanced amounts, the beneficial effects of exercise in diabetes are numerous. Exercise facilitates the utilization of glucose as the main source of energy for contracting muscles and decreases peripheral insulin resistance. Limited epidemiological studies have demonstrated that lack of physical activity may be involved in the epidemic outburst of non-insulin-dependent diabetes mellitus (NIDDM) in some unusual populations. Long-term studies are still needed to show that lifelong physical training and exercise reduce morbidity and mortality in diabetes.