Abstract: Posttraumatic stress disorder (PTSD) and chronic pain are highly comorbid, share overlapping symptoms, and exacerbate and maintain one another, which makes the accurate assessment of symptoms critical to effective clinical care. The present study evaluated the factor structure of the PTSD Checklist for DSM-5 (PCL-5) in a veteran sample with chronic pain and determined the extent to which pain intensity is associated with PCL-5 responses. Participants were a national sample of 384 veterans prescribed long-term opioid therapy who reported moderate or severe pain, experienced a traumatic event, and completed the PCL-5. The majority of the sample identified as White (79.9%) and Male (84.1%). Confirmatory factor analysis was used to evaluate the factor structure of the PCL-5, and measurement invariance testing was used to determine the extent to which pain intensity was associated with how patients responded to the PCL-5. The six-factor anhedonia (χ2=313.45, df = 155, CFI =.969, RMSEA =.052, 90% CI:.043,.060, DRMR =.036, TLI =.95) and seven-factor hybrid (χ2=304.20, df = 149, CFI =.960, RMSEA =.052, 90% CI:.044,.060, SRMR =.036, TLI =.95) models emerged as the best fitting and both exhibited configural, metric and scalar invariance. This suggests that PCL-5 scores can be interpreted similarly among patients with moderate and severe chronic pain and that complex models can be employed to help determine the focus of treatment and track granular changes in PTSD symptoms over time.