To determine the impact of gender-affirming mastectomy on depression, anxiety, and body image. There are many cross-sectional and ad-hoc studies demonstrating the benefits of gender-affirming surgery. There are few prospective investigations of patient-reported outcomes in gender-affirming surgery using validated instruments. In this prospective study, patients presenting to the University of Michigan for gender-affirming Mastectomy were surveyed preoperatively and 6-months postoperatively. Primary outcomes were patient-reported measurements of anxiety measured by General Anxiety Disorder-7, depression measured by Patient Health Questionnaire-9, body image measured by BODY-Q and Body Image Quality of Life Index, psychosocial and sexual functioning measured by BREAST-Q, and satisfaction with decision measured by BREAST-Q. Linear regression analysis was used to control for presence of complication and existing history of mental health conditions. A total of 70 patients completed the study. The average age of participants was 26.7. The mean Patient Health Questionnaire-9 score pre-operatively was 7.8 and postoperatively was 5.4 ( P =0.001). The mean preoperative and postoperative General Anxiety Disorder-7 scores were 7.6 and 4.6, respectively ( P <0.001). There were significant improvements in both psychosocial (35 to 79.2, P <0.001) and sexual (33.9 to 67.2, P< 0.001) functioning related to chest appearance as measured by the BREAST-Q and global psychosocial functioning (-15.6 to +32, P <0.001) as measured by the Body Image Quality of Life Index. Satisfaction with chest contour (14.3 to 93.8, P <0.001) and nipple appearance (29.3 to 85.9, P <0.001) measured by the BODY-Q significantly improved. Patients had a mean satisfaction with outcome score of 93.1. Patients undergoing gender-affirming mastectomy in this single-center prospective study reported significant improvements in anxiety, depression, body image, psychosocial, and sexual functioning after this procedure. Patients were extremely satisfied with the decision to undergo this operation.