BACKGROUND: There are over 150,000 transgender adolescents in the United States, yet research on outcomes following gender-affirming mastectomy in this age group is limited. We evaluated gender-affirming mastectomy incidence, as well as postoperative complications, including regret, in adolescents within our integrated health care system. METHODS: Gender-affirming mastectomies performed from January 1, 2013 - July 31, 2020 in adolescents 12-17 years of age at the time of referral were identified. The incidence of gender-affirming mastectomy was calculated by dividing the number of patients undergoing these procedures by the number of adolescents assigned female at birth ages 12-17 within our system at the beginning of each year and amount of follow-up time within that year. Demographic information, clinical characteristics (comorbidities, mental health history, testosterone use), surgical technique, and complications, including mention of regret, of patients who underwent surgery were summarized. Patients with and without complications were compared to evaluate for differences in demographic or clinical characteristics using chi-squared tests. RESULTS: The incidence of gender-affirming mastectomy increased 13-fold (3.7 to 47.7 per 100,000 person-years) during the study period. Of the 209 patients who underwent surgery, the median age at referral was 16 years (range 12-17) and the most common technique was double-incision (85%). For patients with greater than 1-year follow-up (n=137, 65.6%), at least one complication was found in 7.3% (n=10), which included hematoma (3.6%), infection (2.9%), hypertrophic scars requiring steroid injection (2.9%), seroma (0.7%), and suture granuloma (0.7%); 10.9 % underwent revision (n=15). There were no statistically significant differences in patient demographics and clinical characteristics between those with and without complications (p>0.05). Two patients (0.95%) had documented postoperative regret but neither underwent reversal surgery at follow-up of 3 and 7 years postoperatively. CONCLUSION: Between 2013-2020, we observed a marked increase in gender-affirming mastectomies in adolescents. The prevalence of surgical complications was low and of over 200 adolescents who underwent surgery, only two expressed regret, neither of which underwent a reversal operation. Our study provides useful and positive guidance for adolescent patients, their families, and providers regarding favorable outcomes with gender-affirming mastectomy.