The current study examined whether the Avoidance and Fusion Questionnaire for Youth (AFQ-Y; L. A. Greco, W. Lambert, & R. A. Baer, 2008), a self-report measure of psychological inflexibility for children and adolescents, might be useful for measuring psychological inflexibility for adults. The psychometric properties of the AFQ-Y were examined using data from a college student sample (N = 387) and a clinical sample of patients with anxiety disorders (N = 115). The AFQ-Y, but not the Acceptance and Action Questionnaire-II (AAQ-II; F. W. Bond et al., in press), demonstrated a reading level at or below the recommended 5th or 6th grade reading level. The AFQ-Y also demonstrated adequate reliability (internal consistency), factorial validity, convergent and discriminant validity, and concurrent validity predicting psychological symptoms. Moreover, the AFQ-Y showed incremental validity over the AAQ-II in predicting several psychological symptom domains. Implications for the assessment of psychological inflexibility are discussed. (Contains 2 tables and 2 footnotes.)