Overweight and obesity have reached epidemic dimensions worldwide, mainly due to consumption of high energy diets and increased sedentary behaviour. Overweight and insufficient physical activity are clearly associated with cardiovascular diseases and type 2 diabetes. Evidence is also accumulating that they may also increase cancer risk, particularly in the colon, breast and endometrium. This effect seems to be mediated by alterations in the metabolism of endogenous hormones, including sex steroids and insulin, and levels of insulin-like growth factor(IGF)-I and IGF-binding proteins. In light of the beneficial effects of weight control and physical activity for cancer prevention, a healthy lifestyle, keeping a low body weight and exercising most days of the week, is recommended.