The current study explored the relationships between GPs' beliefs about the cause of obesity and treatment choices. Participants (n = 81) responded to two sets of materials; vignettes featuring obese patients in which the grade and cause of obesity were manipulated, and a survey of beliefs about the causes of obesity. Participants were asked to rate how likely it would be for the patient to receive each of six treatments. Group comparisons, correlational analyses and logistic regression methods were employed. The results revealed that, as obesity increased, participants were more likely to refer patients on for all of the interventions rather than to 'watch and wait' and provide advice directly. The grade of obesity explained the most variance in ratings of treatment choice, suggesting that GPs' decisions are in line with current guidelines (NICE, 2006). Participants were more likely to agree with statements supporting an internal locus of control in the cause of obesity (LoCI) than an external locus of control (LoCE). Participants' beliefs that obesity is caused by LoCE factors were associated with them being more likely to refer for both medical interventions (pharmacological/surgical) and behavioural-based treatments (nurse/dietician/clinical psychology). Participants' beliefs that obesity is caused by LoCI factors were associated with GPs being more likely to 'watch and wait'. Previous research suggests that patients are more likely to believe obesity is out of their control (Ogden et al, 2001). The current study therefore suggests that GPs are more likely to work directly with patients who have different beliefs about the cause of obesity to their own. The implications of this finding for future research and practice are discussed.