Epidemiological research has consistently shown that physical activity decreases the risk of coronary heart disease, hypertension and stroke. The finding that a low level of physical activity is a major determinant of the growing epidemics of obesity is also firm and consistent. The direct association existing between a sedentary lifestyle and the incidence of diabetes mellitus is solid and of great importance for public health. Additional benefits from a a physically active lifestyle are a reduction in the incidence and prevalence of osteoporosis, lower risk of falls and fractures in the elderly, and a lower risk of anxiety and depression. Although evidence is less consistent, low levels of physical activity have been related to a higher risk of colon, breast and lung cancer. Some preliminary evidence relates physical activity with a lower risk of dementia. During the last three decades a huge amount of epidemiological research has led to uniform conclusions about the benefits of a physically active lifestyle. In spite of this fact, the prevalence of sedentary lifestyles is rising. Therefore, health promotion interventions are urgently needed to reach the objective of engaging in regular and moderate physical activity for at least 30 minutes per day in most, preferably all, days of the week.