The current wars in Iraq and Afghanistan are producing large numbers of veterans who have experienced a variety of combat stressors. The potential impact of combat exposure has been established, including significant rates of posttraumatic stress disorder (PTSD). Limited research has examined potential differences between veteran groups and one study to date has examined differences between eras in terms of treatment response. The present study seeks to examine cohort differences between Operation Enduring Freedom and Operation Iraqi Freedom veterans and Vietnam veterans (N = 101) before and after completing treatment for PTSD using cognitive processing therapy. Findings suggest that veterans from these eras responded differently to treatment and there are multiple variables that should be considered in future cohort studies.