Given that retention rates for weight-loss trials have not significantly improved in the past 20 years, identifying effective techniques to enhance retention is critical. This paper describes a conceptual and practical advance that may have improved retention in a behavioral weight-loss trial-the novel application of motivational interviewing techniques to diffuse ambivalence during interactive group-based orientation sessions prior to randomization. These orientation sessions addressed ambivalence about making eating and exercise behavior changes, ambivalence about joining a randomized controlled trial, and unrealistic weight-loss expectations. During these sessions, overweight and obese men and women learned about the health benefits of modest weight loss as well as trial design, the importance of a control condition, random assignment and the impact of dropouts. Participants were then divided into groups of three or four, and asked to generate two pros and two cons of being assigned to a control condition and an active condition. Participants shared their pros and cons with the larger group, while the investigator asked open-ended questions, engaged in reflective listening and avoided taking a 'pro-change' position. Retention was high, with 96% of the participants (N = 162) completing 18-month clinic visits.