Objectives. There were three objectives of this dissertation: (1) compare rates of psychological outcomes between battle and non-battle injury; (2) assess injury-specific predictors of post-traumatic stress disorder (PTSD) and other psychological outcomes; and (3) examine the role of traumatic brain injury in the development of psychological outcomes. Methods. Three population-based retrospective studies were conducted utilizing data from the Navy and Marine Corps Combat Trauma Registry (CTR), the Career History Archival Medical and Personnel System (CHAMPS), and, for objective one only, Post Deployment Health Assessments (PDHA). The Navy-Marine Corps CTR contains information on clinical encounters during Operation Iraqi Freedom for battle and non-battle injury. Male U.S. combatants injured between September 2004 and February 2005 were included in the study. Outcome data through November 2006 were abstracted from CHAMPS in the form of ICD-9 codes indicating mental health diagnosis (ICD-9 290-319) and specifically PTSD (ICD-9 309.81). For objective one, self-reported mental health symptoms from the PDHA were also utilized as outcome data. Results. Battle injuries had higher rates of PTSD, other mental health diagnoses, and self-reported mental health symptoms when compared to non-battle injuries, with the greatest effect observed with increasing battle injury severity. Overall the rate of PTSD was 17.0% among battle injuries and 5.1% among non-battle injuries, and rates of any mental health outcome were 31.3% and 14.2% among battle and non-battle injuries, respectively. Among battle injuries, injury severity predicted both PTSD and any mental health outcome. Any mental health outcome was also predicted by gunshot wounds and diastolic blood pressure; the effect of diastolic blood pressure was modified by injury severity. Post-injury heart rate did not predict PTSD or any mental health outcome. The rate of traumatic brain injury (TBI) among battle injuries was 21.0%, and TBI prevalence was associated with blast injury. When examining injuries of moderate or higher severity, TBI was associated with lower rates of mental health diagnosis compared to non-head injuries. Conclusions. Battle injuries were associated with high rates of PTSD and other psychological outcomes, and important predictors included injury severity and gunshot wounds. Lower rates of mental health diagnoses among those with TBI may be due to symptom overlap between TBI and many psychological disorders. Unmeasured confounding effects of combat exposure and medical utilization may have influenced the results.