Objective: The purpose of this study was to examine the effects of changes in body image psychological flexibility over the course of treatment on various outcome variables. Method: Participants included 103 female, residential patients diagnosed with an eating disorder. Pretreatment and posttreatment data were collected that examined body image psychological flexibility, general psychological flexibility, symptom severity, and other outcome variables. Results: Changes in body image psychological flexibility significantly predicted changes in all outcome measures except for obsessive-compulsive symptoms after controlling for body mass index, depression, and anxiety. Additionally, these results were maintained after controlling for general psychological flexibility, contributing to the incremental validity of the BI-AAQ. Discussion: This study suggests that changes in body image psychological flexibility meaningfully predict changes in various treatment outcomes of interest, including eating disorder risk, quality of life, and general mental health. Findings indicate that body image psychological flexibility might be a viable target for eating disorder treatment.