© 2016, BMJ Publishing Group. All rights reserved. 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.