Primary care providers can use behavioral lifestyle interventions to effectively treat children with overweight and obesity, but implementing these interventions is challenging. Most childhood obesity intervention evaluation studies focus on effectiveness. Few studies describe implementation. Our goal was to evaluate critical components of a childhood obesity intervention in primary care. We conducted a pilot implementation study of an existing structured lifestyle intervention in the Canton of Bern, Switzerland from 2013 to 2015. The intervention consisted of 10 sessions, led by a primary care physician. It included children aged 6-8 years old, with BMI over the 90th age-adjusted percentile. We used the Reach, Effectiveness, Adoption, Implementation and Maintenance (RE-AIM) evaluation framework to describe the pilot implementation study. We stratified description of RE-AIM components at the patient- and physician-level. For Reach: 864 children were screened; 65 were overweight; 394 physicians were invited to participate in the study. For Effectiveness: BMI z-score significantly decreased (-5.6%, p = 0.01). For Adoption: 14 participating physicians treated 26 patients. Implementation: the mean number of consultations was 8. For Maintenance: 9 (35%) children discontinued the intervention; 7 (50%) of physicians continued to apply at least one component of the intervention. The summarized components of the program within the RE-AIM framework suggest the program was successful. Stakeholders can use our results if they intend to disseminate and evaluate similar interventions in different settings.