To dissect the mechanisms involved in the metabolic disorders associated with BBS, we assessed the development of obesity in multiple BBS mouse models developed in our laboratory. We found that BBS mice are hyperphagic, have low motor activity, and elevated circulating levels of leptin. The effect of exogenous leptin on body weight and food intake is attenuated in BBS mice, suggesting that leptin resistance contributes to hyperleptinemia and obesity in these mice.