(D2/3R) binding in the striatum, an important component of the brain reward system [1–3]. The neurotransmitter dopamine is important for the reinforcing value of food and it has been shown that food can induce a release of endogenous dopamine in the striatum [4]. Obese individuals are thought to be more sensitive to food reinforcement than those who are non-obese. This may underlie the notion that obese humans experience an increased craving for food. In addition, striatal D2/3R availability has been linked to craving and dietinduced obesity [5]. Therefore, it is plausible that dopaminerelated mechanisms linked to craving and impulsiveness play a role in the development and pathophysiology of obesity. At present, it is unclear whether lower D2/3R availability is a cause or an effect of obesity. If the latter is true, one would expect that the reduced D2/3R availability observed in obese humans is reversed following the loss of a clinically significant fat mass or during a hypoenergetic state. Obesity is associated with insulin resistance. Insulin receptors are widely expressed in the human brain, and a relationship between insulin sensitivity and central dopamine signalling has been suggested [6]. It needs to be determined, therefore, whether the striatal D2/3R binding potential correlates with hepatic or peripheral insulin sensitivity. To determine whether the previously reported reduction in D2/3R availability in obese humans is reversible, we studied striatal D2/3R availability before and 6 weeks after Roux-en-Y gastric bypass (RYGB) surgery in 19 morbidly obese women. Eighteen of these patients participated in a study on the short-term metabolic effects of RYGB surgery (NTR1548; for one additional patient only single photon emission computed tomography [SPECT] data could be acquired)[3]. Informed consent was obtained from all participants and the study was approved by the local medical ethics committee of the Academic Medical Center in Amsterdam. We assumed that a difference of 15% in D2/3R availability would be of clinical