Post-traumatic stress disorder (PTSD) diagnosis requires first identifying a traumatic event, but very few studies have evaluated methods of potential traumatic event assessment and their impact on PTSD diagnosis. The authors compared a behaviorally specific comprehensive multiple-item traumatic event measure with a single-item measure to determine their impact on traumatic event identification and subsequent PTSD diagnosis. In a within-subject, counterbalanced design, the Traumatic Life Events Questionnaire (TLEQ; E. S. Kubany et al., 2000) was compared with the single-question traumatic event assessment in the Structured Clinical Interview for DSM-IV (SCID; M. B. First, R. L. Spitzer, M. Gibbon, & J. B. W. Williams, 1998) in 129 participants in opioid-dependence treatment. The TLEQ produced a 9-fold higher rate of traumatic events reported by the participants, compared with the SCID. As a result, PTSD diagnoses in the sample increased to 33% after the TLEQ measure from 24% after the SCID. The increase in potential traumatic event identification and PTSD diagnosis was greater in women than in men. This study provides strong support for the use of comprehensive traumatic event assessments to measure traumatic events and PTSD diagnoses, particularly in women.