Objective: To understand psychosocial functioning before and after gender-affirming facial feminization surgery (FFS) as well as identify predictors of postoperative psychosocial functioning., Summary Background Data: Few investigations have rigorously explored the impact of gender-affirming FFS on psychosocial functioning in transgender and gender non-binary (TGNB) individuals. This knowledge gap hinders the identification of methods to optimize mental health quality-of-life outcomes after FFS and carries repercussions for access to care., Methods: Adult TGNB participants awaiting gender-affirming FFS were prospectively enrolled and administered Patient-Reported Outcomes Measurement Information System (PROMIS) instruments assessing anxiety, anger, depression, global mental and physical health, positive affect, emotional support, social isolation, companionship, and meaning and purpose before and 3-6 months after FFS. Paired t-tests compared pre- and postoperative scores. Multivariable linear models identified predictors of postoperative psychosocial outcomes., Results: Among the domains, psychosocial scores improved for anxiety, depression, global mental health, social isolation, and positive affect after FFS. When accounting for potential variables contributing to postoperative psychosocial scores including other gender-affirming surgeries, hormone therapy duration, and private versus public insurance type, we found that preoperative depression scores independently predicted the variance in all other postoperative scores with global mental health (β=-0.52, 95%CI -0.58--0.31 P<0.001), anxiety (β=0.40, 95% CI 0.21-0.51, P<0.001), and meaning and purpose (β=-0.52, 95% CI -0.78--0.42 P<0.001) as the strongest models., Conclusions: This study suggests that gender-affirming FFS improves psychosocial functioning; however, such improvements are highly influenced by the baseline psychological functioning of each individual. These findings indicate that preoperative psychological functioning may be a potential avenue for improving outcomes after FFS via perioperative psychological interventions., Competing Interests: Conflict of Interest Disclosures: JCL is supported by the National Institutes of Health/National Institute for Dental and Craniofacial Research R01 DE028098 and R01 DE029234. JCL is a medical education consultant for Stryker., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)