A link has been established between obesity and osteoarthritis (OA), but the precise relationship has yet to be defined. OA has a multifactorial etiology, and obesity is consistently identified as an independent and modifiable risk factor. The biomechanical relationship is intuitive: increased loads on articular cartilage cause subsequent wear and cartilage breakdown. Less intuitive, and possibly more important, are the systemic effects of obesity on OA. Promising investigations into relationships between lipid metabolism and OA have been rarely reported in the orthopaedic literature. These reports argue that, in obese patients, weight loss may not only help prevent OA but also may be an effective treatment strategy. Orthopaedic surgeons should be aware of the biomechanical and systemic implications of obesity with respect to OA so that patients may be counseled accordingly.