The Generalized Pliance Questionnaire (GPQ) was originally validated against measures of psychological flexibility and psychological distress. However, measures which have substantial conceptual overlap with the GPQ (e.g., the Need to Belong Scale [NTBS], Brief Fear of Negative Evaluation Scale [BFNE]) were not examined. The present study seeks to investigate the construct validity of the GPQ-9. As expected, data from a survey of 272 participants indicated significant large correlations between the GPQ-9 and NTBS and BFNE respectively. The results of a confirmatory factor analysis confirmed the unidimensional structure of the GPQ-9. A structural equation model revealed that the BFNE (and not the GPQ-9 or NTBS) was significantly associated with psychological flexibility and psychological distress. Implications of these tentative preliminary findings suggest that the GPQ may be a more sensitive measure than the BFNE for ACT research.