PROJECT SUMMARY Severe obesity, defined as ≥ 120% of the 95th percentile of body mass index (BMI) adjusted for age and sex or a BMI >35 kg/m2 is the fastest growing subcategory of obesity in the United States (US) pediatric population. Approximately 9% of 12-19 year-olds have severe obesity, triple the prevalence in 1988-1994. Even more concerning, almost 12% of Non-Hispanic Black and 9% of Hispanic adolescents ages 12-19 have severe obesity compared to 7% of their non-Hispanic white counterparts. Metabolic and bariatric surgery (MBS) is shown to be safe and efficacious in treating adolescents (defined as ages 13-18 for this application) with severe obesity. Yet national adolescent MBS rates have not increased at the same rate of that of the severe obesity epidemic, and short-and long-term attrition (those who qualify but do not follow through with MBS and those who do not return for care after MBS) remains a significant challenge in this patient population. Alternatively, weight-loss behavioral/lifestyle and pharmacotherapy treatment programs in inpatient and ambulatory settings have not reported similar sustained weight loss trajectories, particularly in the long-term. Behavioral/lifestyle programs teach the necessary modifications to sustain successful weight loss, but there is no standardized pre-and post- operative lifestyle intervention that is offered to adolescent MBS patients to support these behavioral changes. As such, we propose the following mixed methods specific aims: AIM 1. Generate qualitative data necessary to adapt an existing evidence-based healthy lifestyle behavioral intervention’s content, strategies and delivery methods to explicitly support pre- and post-MBS, ethnically diverse (non-Hispanic white and black; Hispanic, other), adolescent patients and their families. This formative research will include focus groups, and key informant interviews with adolescents, parents, and clinical team members. AIM 2. Adapt the healthy lifestyle behavioral intervention (referenced in AIM 1), as informed by AIM 1 data (and analyses), to support pre-and post-MBS among ethnically diverse adolescent patients and their families. AIM 3. Conduct a proof-of-concept study to assess feasibility, acceptability and effectiveness of an MBS-supported healthy lifestyle behavioral intervention (adapted in AIM 2) among adolescent patients, their families, and their clinical team. We will iteratively analyze the AIM 1 qualitative data until no new concepts emerge from later interviews/discussions, and the resulting themes are considered “saturated” by the data analysts. Results from this study will inform the development of a future randomized controlled trial to test the MBS-lifestyle intervention(s) versus standard of care.