Osteoarthritis (OA) has become one of the leading causes of disability in the United States. Mechanical forces exerted on the joints are a significant cause of OA and one of the most modifiable risk factors. As determined by body mass index (BMI), 34 million US adults are obese, and 13 million of these are morbidly obese. Female sex, lower educational levels, obesity, and poor muscular strength are associated with symptomatic disease and subsequent disability. Recently, genetics has been shown to be a significant factor in the disease process. March and Bagga (Med J Aust. 2004; 180 (5 suppl): S6-S10) showed that the risk for knee OA increased by 36% for every 2 units of BMI (5 kg) of weight gain. Bariatric surgery results in a mean weight loss of 44 kg (97 lb). Eighty-nine percent of patients had complete relief of pain caused by OA in at least one joint after undergoing bariatric surgery.