OBJECTIVES:Internationally, general practitioners (GPs) are being encouraged to take an active role in the care of their patients with obesity, but as yet there are few tools for them to implement within their clinics. This study assessed the self-efficacy and confidence of GPs before and after implementing a weight management programme in their practice. DESIGN:Nested mixed methods study within a 6-month feasibility trial. SETTING:4 urban general practices and 1 rural general practice in Australia. PARTICIPANTS:All vocationally registered GPs in the local region were eligible and invited to participate; 12 GPs were recruited and 11 completed the study. INTERVENTIONS:The Change Programme is a structured GP-delivered weight management programme that uses the therapeutic relationship between the patient and their GP to provide holistic and person-centred care. It is an evidence-based programme founded on Australian guidelines for the management of obesity in primary care. PRIMARY OUTCOME MEASURES:Self-efficacy and confidence of the GPs when managing obesity was measured using a quantitative survey consisting of Likert scales in conjunction with pro forma interviews. RESULTS:In line with social cognitive theory, GPs who experienced performance mastery during the pilot intervention had an increase in their confidence and self-efficacy. In particular, confidence in assisting and arranging care for patients was improved as demonstrated in the survey and supported by the qualitative data. Most importantly from the qualitative data, GPs described changing their usual practice and felt more confident to discuss obesity with all of their patients. CONCLUSIONS:A structured management tool for obesity care in general practice can improve GP confidence and self-efficacy in managing obesity. Enhancing GP 'professional self-efficacy' is the first step to improving obesity management within general practice. TRIAL REGISTRATION NUMBER:ACTRN12614001192673; Results.