|Posttraumatic stress disorder (PTSD) is commonly assessed with self-rated or clinician-rated measures. Self-rated measures are more widely used, but clinician-rated measures are considered the gold standard for diagnosis. Although scores from these distinct PTSD assessment methods are strongly associated, they are often discrepant for individual symptoms, total symptom severity, and PTSD diagnostic status. To date, no known studies have empirically identified the sources of these discrepancies. Accordingly, the present study had three aims: (a) replicate previously identified discrepancies; (b) examine the contribution of several objective predictors of discrepancies, including negative response bias, careless or random responding, conscientiousness, neuroticism, and verbal IQ; and (c) identify subjective sources of discrepancies through qualitative analysis of participant feedback. Trauma-exposed undergraduates (N= 60) were administered the PTSD Checklist for DSM-5 (PCL-5), the Clinician-Administered PTSD Scale for DSM-5 (CAPS-5), and several other self-rated measures. Participants then provided open-ended feedback regarding their attributions for their discrepant symptom scores on the PCL-5 versus CAPS-5. Results indicated that the most discrepant symptoms were cued physical reactions, avoiding internal reminders, blame, loss of interest, and hypervigilance. Further, in general, objective predictors were only weakly associated with discrepancies, and for total discrepancy, neuroticism was the only significant predictor. Last, qualitative analyses revealed that the most commonly reported reasons for discrepancies were time-frame reminders, comprehension of symptoms, trauma-related attribution errors, increased awareness, and general errors. These findings elucidate the nature and sources of discordance between the PCL-5 and the CAPS-5, and will inform the use and interpretation of these measures in a wide range of clinical and research applications.