BACKGROUND: Although transgender surgery constitutes a growing field within plastic surgery, prospective studies on masculinizing mastectomies are lacking. The objectives of the present study were to prospectively follow a cohort of transmen undergoing mastectomy to assess technical and self-reported outcomes and to evaluate surgical decision-making. METHODS: Fifty-four transmen were recruited during a 10-month period at the Department of Plastic Surgery of the Centre of Expertise on Gender Dysphoria. Preoperative assessment included standardized chest examination. Six months postoperatively, participants rated their satisfaction with surgery, and 12-month postoperative surgical outcomes were reviewed independently. Surgical decision-making was evaluated by comparing indications and outcomes per technique, and assessing the clinical validity of the most-used decision aid (using the Cohen's kappa statistic). RESULTS: One periareolar mastectomy, 26 concentric circular mastectomies, and 22 inframammary skin resections with free nipple graft were performed in the authors' cohort. Five participants were still to be operated on. Concentric circular mastectomy was performed in smaller or medium-size breasts with low ptosis grade and good elasticity, whereas the inframammary skin resection group showed a wider range of physical characteristics. Despite being performed in better quality breasts, concentric circular mastectomy was associated with more secondary corrections (38.5 percent), dehiscence, seroma, and lower postoperative satisfaction compared with inframammary skin resections. Clinical decision-making was generally in line with the published decision aid. CONCLUSIONS: Compared with inframammary skin resections, concentric circular mastectomy-despite being performed in favorable breast types-appears to produce poorer technical and self-reported outcomes. Surgical indications and preoperative counseling regarding secondary corrections may therefore be subject to improvement. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.