Background: Sex differences in body composition emerge during adolescence and persist throughout the life course. Lifestyle intervention in youth can alter body composition but little is known about sex differences in response to lifestyle in the pediatric population. Therefore, the purpose of this systematic review was to evaluate sex differences in measures of adiposity following lifestyle interventions among children and adolescents. Methods: Electronic databases (PubMed, Web of Science, and MEDLINE/Ovid) were systematically searched from inception through March 2021. Eligibility criteria included: randomized controlled trials, published in English, lifestyle intervention with both nutrition and physical activity components, children and adolescents aged 6-18 years old, and at least one measure of adiposity. Abstracts and full-text articles were reviewed by three independent reviewers. Data were extracted into a standardized spreadsheet. A significant intervention effect or differential response between the sexes was determined by comparison of mean differences between intervention and control groups with a p-value<0.05. Results: Of 111 full-text articles reviewed, 59 (53%) were included, of which 36 (61%) reported statistically significant intervention effects on adiposity. Of these 36 studies, BMI z-score was the most frequent adiposity measure showing significant reductions (56%, n=20), followed by BMI (36%, n=13), waist circumference (WC; 33%, n=12), BMI-standard deviation score (BMI-SDS; 14%, n=5), and waist-to-hip ratio (8%, n=3). Eleven studies reported significant decreases in body fat percentage (91%, n=10), fat mass (46%, n=5), and abdominal adiposity (18%, n=2). Only four studies (11.1%) evaluated sex differences in response to lifestyle intervention. One of these studies found significantly greater reductions in BMI z-score among females compared to males. Another study demonstrated that gender was a significant moderator of intervention effects with females showing reductions in BMI, BMI%, BMI z-score, and WC, whereas males demonstrated an increase in all BMI measures and WC. Despite these differences, only the pairwise comparison for WC was trending significant. In contrast, one of these four studies demonstrated a significant within-group intervention effect for BMI, BMI z-scores, and WC z-scores among males but not in females; however, between-group differences were not analyzed. In the last study, males had a greater reduction in BMI-SDS than females following lifestyle intervention; however, these differences were not statistically significant. Conclusion: In conclusion, almost two-thirds (61%) of lifestyle intervention studies demonstrated significant improvements in adiposity among children and adolescents. Few studies (11.1%) examined sex differences in adiposity outcomes in response to lifestyle intervention, reporting conflicting results. It is important to evaluate sex differences in response to lifestyle interventions to better inform health promotion programs. The next step is to conduct a meta-analysis to determine the effect of lifestyle interventions on sex differences in adiposity outcome measures among all of the studies included in the systematic review.