Background Primary care physicians are being asked to counsel their patients on obesity and weight management. Few physicians conduct weight loss counselling citing barriers, among them a lack of training and confidence. Our objective was to pilot test the effectiveness of a 3-h interactive obesity-counselling workshop for resident physicians based on motivational interviewing (MI) techniques. Design This study used a pretest/post-test crosssectional design. A convenience sample of resident physicians was invited to participate. Participating resident physicians completed a preintervention and postintervention questionnaire to assess their knowledge, beliefs and confidence in obesity counselling. MI techniques taught in the intervention were evaluated by audio recording interviews with a standardised patient (SP) pre intervention and post intervention. Audio recordings were transcribed and coded by two independent coders using a validated assessment tool. Paired t tests were used to assess preintervention and postintervention differences. Results Eight-six residents attended the workshop. At baseline, the majority (71%) felt that there is not enough time to counsel patients about obesity and only 24% felt that residency trained them to counsel. After the intervention, knowledge and confidence in counselling increased (p<0.001). Among the 55 residents with complete pre-post SP interview data, MI adherent statements increased from a mean of 2.88 to 5.42 while the MI non-adherent statements decreased from 6.73 to 2.33 (p<0.001). Conclusions After a brief workshop to train physicians to counsel on obesity-related behaviours, residents improved their counselling skills and felt more confident on counselling patients. Future studies are needed to assess whether these gains are sustained over time.