The evidence linking overweight and obesity with morbidity and mortality are reviewed. The terms" overweight" and'obesity'are defined. The role of body fat distribution in predicting health risk is discussed along with obesity-associated diseases such as type 2 diabetes mellitus, coronary heart disease, sleep apnoea, pulmonary dysfunction, stroke, gallbladder disease, liver diseases, musculoskeletal disease, fertility disorders and cancer, are discussed. The effects of intentional weight loss on morbidity and mortality are also tackled. It is concluded that high levels of body weight and body fat are associated with an increased risk of development of adverse health consequences. Moderating factors such as diet, body fat distribution and physical activity can have an impact on the risks of overweight for a given individual.