The Adverse Childhood Experience (ACE) Questionnaire is one of the most widely used assessments for trauma exposure and adversity experienced during the first 18 years of life (Felitti et al., 1998 Felitti, V. J, Anda, R. F, Nordenberg, D., Williamson, D. F, Spitz, A. M, Edwards, V., Koss, M. P, & Marks, J. S, (1998). Relationship of childhood abuse and household dysfunction to many of the leading causes of death in adults: The Adverse childhood experiences (ACE) study. American Journal of Preventive Medicine, 4, 14, 245–258. https://doi.org/10.1016/S0749-3797(98)00017-8 http://doi.org/10.1016/j.amepre.2019.04.001[Crossref], [Web of Science ®] , [Google Scholar]; Kia-Keating et al., 2019). While the ACE Questionnaire has shown to have good reliability and validity, inconsistencies have been demonstrated for the test-retest form of reliability (MacKenzie et al., 2005 MacKenzie, S., Podsakoff, P., & Jarvis, C. (2005). The problem of measurement model misspecification in behavioral and organizational research and some recommended solutions. Journal of Applied Psychology, 4, 90, 710–730. https://doi.org/10.1037/0021-9010.90.4.710[Crossref], [Web of Science ®] , [Google Scholar]; Pinto et al., 2014 Pinto, R., Correia, L., & Maia, A. (2014). Assessing the reliability of retrospective reports of adverse childhood experiences among adolescents with documented childhood maltreatment. Journal of Family Violence, 4, 29, 431–438. https://doi.org/10.1007/s10896-014-9602-9[Crossref], [Web of Science ®] , [Google Scholar]; Zanotti et al., 2018 Zanotti, D. C., Kaier, E., Vanasse, R., Davis, J. L., Strunk, K. C., & DeMarni Cromer, L. (2018). Examination of the test-retest reliability of the ACE-SQ in a sample of college athletes. Psychological Trauma: Theory, Research, Practice, and Policy, 5, 10, 559–562. https://doi.org/10.1037/tra0000299[Crossref], [Web of Science ®] , [Google Scholar]). To address the lack of consensus on the test-retest reliability of the ACE Questionnaire and the appropriateness for use with adolescents, the current study examined test-retest reliability of the ACE measure for a small group of adolescents in residential treatment. Participants (n = 20) completed the ACE during week 1 and were later assessed at week 9. The test-retest reliability of the ACE was very high (r = 0.913), thereby supporting the overall reliability of the ACE questionnaire and its effectiveness in identifying baseline trauma. However, the results indicate that adolescents might not fully understand their past trauma experiences prior to receiving trauma-focused treatment. Potential explanations of unreliable reporting of ACEs, counseling implications and recommendations for multiple administrations are discussed.