Reduced levels of BDNF in mice cause obesity and behavioral abnormalities including increased aggression and hyperactivity. While it has been shown that the obesity is in part caused by increased food consumption it is still not clear whether defects in other mechanisms involved in the control of body weight homeostasis can also affect this phenotype. Here we report that mice with reduced levels of BDNF do not develop obesity and have normal blood glucose levels if fed over a prolonged period of time the amount of food that control mice usually consume. Thus, hyperphagia appears to be the primary cause of obesity development rather than changes in mechanisms controlling metabolism.