Thin ideal internalization is a risk factor for disordered eating behaviors, poor body image, and eating disorders (EDs). This paper evaluated the psychometric properties of a novel measure, the Perceived Benefits of Thinness Scale (PBTS), which assesses how individuals feel being thinner would affect various aspects of their lives. Three separate studies with unique samples of college-aged women over 18 years were conducted to assess reliability and validity. In Study 1, exploratory and confirmatory factor analyses suggested all PBTS items loaded onto one factor that was distinct from a measure of weight and shape concerns. A large correlation between changes in PTBS scores and changes in ED psychopathology scores over 8 months (r = .57, p < .01) suggested sensitivity to change. Greater severity in ED pathology was also associated with higher scores on the PBTS. In Study 2, the PBTS showed good test-retest reliability (r = .84, p < .001) and, in Study 3, expected correlations with existing measures of thin ideal internalization (rs = .38-.60, ps < .001). Overall, the PBTS displayed good factor structure, reliability, concurrent validity, and sensitivity to change. By emphasizing social, emotional, and quality of life benefits, the PBTS may serve clinicians, researchers, and patients in understanding thin ideal internalization and associated ED risk.