BACKGROUND: Child and adolescent overweight and obesity have increased globally and are associated with significant short- and long-term health consequences. OBJECTIVES: To assess the effects of surgery for treating obesity in childhood and adolescence. SEARCH METHODS: For this update, we searched Cochrane Central Register of Controlled Trials, MEDLINE, Latin American and Caribbean Health Science Information database (LILACS), World Health Organization International Clinical Trials Registry Platform (ICTRP)and ClinicalTrials.gov on 20 August 2021 (date of the last search for all databases). We did not apply language restrictions. We checked references of identified studies and systematic reviews. SELECTION CRITERIA: We selected randomised controlled trials (RCTs) of surgical interventions for treating obesity in children and adolescents (age < 18 years) with a minimum of six months of follow-up. We excluded interventions that specifically dealt with the treatment of eating disorders or type 2 diabetes, or which included participants with a secondary or syndromic cause of obesity, or who were pregnant. DATA COLLECTION AND ANALYSIS: We used standard methodological procedures expected by Cochrane. Two review authors independently extracted data and assessed the risk of bias using the Cochrane Risk of Bias 2.0 tool. Where necessary, we contacted authors for additional information. MAIN RESULTS: With this update, we did not find any new RCTs. Therefore, this updated review still includes a single RCT (a total of 50 participants, 25 in both the intervention and comparator groups). The intervention focused on laparoscopic adjustable gastric banding surgery, which was compared to a control group receiving a multi-component lifestyle programme. The participating population consisted of Australian adolescents (a higher proportion of girls than boys) aged 14 to 18 years, with a mean age of 16.5 and 16.6 years in the gastric banding and lifestyle groups, respectively. The trial was conducted in a private hospital, receiving funding from the gastric banding manufacturer. For most of the outcomes, we identified a high risk of bias, mainly due to bias due to missing outcome data. Laparoscopic gastric banding surgery may reduce BMI by a mean difference (MD) of -11.40 kg/m (95% CI -13.22 to -9.58) and weight by -31.60 kg (95% CI -36.66 to -26.54) compared to a multi-component lifestyle programme at two years follow-up. The evidence is very uncertain due to serious imprecision and a high risk of bias. Adverse events were reported in 12/25 (48%) participants in the intervention group compared to 11/25 (44%) in the control group. A total of 28% of the adolescents undergoing gastric banding required revisional surgery. The evidence is very uncertain due to serious imprecision and a high risk of bias. At two years of follow-up, laparoscopic gastric banding surgery may increase health-related quality of life in the physical functioning scores by an MD of 16.30 (95% CI 4.90 to 27.70) and change in health scores by an MD of 0.82 (95% CI 0.18 to 1.46) compared to the lifestyle group. The evidence is very uncertain due to serious imprecision and a high risk of bias. No data were reported for all-cause mortality, behaviour change, participants' views of the intervention and socioeconomic effects. Finally, we have identified three ongoing RCTs that are evaluating the efficacy and safety of metabolic and bariatric surgery in children and adolescents. AUTHORS' CONCLUSIONS: Laparoscopic gastric banding led to greater body weight loss compared to a multi-component lifestyle program in one small study with 50 participants. These results have very limited application, primarily due to more recent recommendations derived from observation studies to avoid the use of banding in youth due to long-term reoperation rates. This systematic review update still highlights the lack of RCTs in this field. The authors are concerned that there may be ethical barriers to RTCs in this field, despite the lack of other effective therapies for severe obesity in children and adolescents and the significant morbidity and premature mortality caused by childhood obesity. Nevertheless, future studies, whether pre-registered and planned non-randomised or pragmatic randomised trials, should assess the impact of the surgical procedure and post-operative care to minimise adverse events, including the need for post-operative adjustments and revisional surgery. Long-term follow-up is also critical to comprehensively assess the impact of surgery as participants enter adulthood.