The Clinician-Administered PTSD Scale (CAPS) is used to measure posttraumatic stress symptoms (PTSS) and diagnose posttraumatic stress disorder (PTSD). However, its use, particularly in settings involving longitudinal assessment, has been complicated by changes in the diagnostic criteria between the fourth and fifth editions of the Diagnostic and Statistical Manual of Mental Disorders (i.e., DSM-IV and DSM-5, respectively). The current sample included trauma-exposed U.S. veterans who were deployed in support of military operations following the September 11, 2001, terrorist attacks (N = 371) and were enrolled in a longitudinal study focused on deployment-related stress and traumatic brain injury. A hybrid clinical interview using item wording from the CAPS for DSM-IV (CAPS-IV) with the addition of items unique to the CAPS for DSM-5 (CAPS-5) was used to assess both DSM-IV and DSM-5 PTSD diagnostic criteria, allowing for the calculation of separate total scores and diagnoses. Diagnostic agreement, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and interrater reliability between CAPS-IV and CAPS-5 were evaluated for the entire sample and stratified by gender. We found high diagnostic agreement (92.9%-95.4%), sensitivity (94.4%-98.2%), specificity (91.7%-92.8%), PPV (89.5%-93.0%), NPV (95.7%-98.1%), and interrater reliability,κ = 0.86-0.91,) for both men and women. The current study supports the use of a hybrid PTSD diagnostic interview assessing both DSM-IV and DSM-5 diagnostic criteria, particularly in situations such as longitudinal studies that may require a feasible method of incorporating changes in diagnostic criteria from the DSM-IV to the DSM-5.