Motivational interviewing (MI) is devised to change unhealthy behaviors by increasing motivation. We adapted MI to a group format for the treatment of relapse during the behavioral treatment of obesity and performed a clinical audit to evaluate its effectiveness in stopping weight regain. The program was structured in seven weekly sessions, plus a 6-month follow-up. Patients ( = 86) completed a questionnaire on motivation to change in both healthy diet and physical activity, and a self-reported measurement of calorie intake and physical activity at baseline, at program end and at 6-month follow-up. The attendance to the program was high, with only 13 patients (15%) not completing the program and 24% not attending the 6-month follow-up. By the end of follow up, the prevalence of patients in either precontemplation or contemplation was reduced from over 60% at enrollment to approximately 20%, whereas the sum of patients in action or maintenance stages was increased from 9.5% in healthy diet and 14% in physical activity to 39.7% and 41.3%, respectively. These changes translated into significant behavioral changes (mean calorie intake, -13%; total physical activity, +125%; sedentary time, -8%) and finally into reduced body weight ( -3%). We conclude that MI programs adapted for groups may be used to stop relapse in individuals following a behavioral intervention for obesity.