Osteoarthritis (OA) is the most common articular disease of the developed world and a leading cause of chronic disability, mostly as a consequence of the knee OA and/or hip OA. In spite of misrecognition of the exact cause, a number of studies have shown that obesity represents one of the most important risk factors and it is also a predictor for progression of OA, especially of a knee joint and less of the hip joint. Relationship between body mass index (BMI) and OA of the knee is mainly linear, and duration of increasedjoint loading or gaining weight is also significant. Studies about obesity and hand OA are contradictory. Risk gradient for BMI and the hip OA is somewhere between the knee and the hand gradient. Disability may be significantly relieved if a body weight is decreased for more than 5.1%. Twenty seven percent of cases of hip arthroplasty and 69% knee arthroplasty may be attributed to obesity. Nonpharmacologic treatment of OA includes treatment of obesity.