This systematic review discusses whether the diagnosis of Traumatic Brain Injury (TBI) alone or a co-occurring TBI and Post Traumatic Stress Disorder (TBI+PTSD) has a greater effect on Executive Function (EF) skills of United States Veterans. A comprehensive, electronic literary search was conducted between the years of 2009 and 2014 to distinguish relevant peer-reviewed journals. The studies that met the inclusion criteria were evaluated for quality and then classified accordingly. The review found twelve studies related to the research question, involving 1,593 veterans diagnosed with TBI or TBI+PTSD. There was significant variability in methodologies that were used to assess EFs (e.g., standardized assessment versus self-report surveys, which specific EFs were measured, etc.). The majority of studies found that veterans with TBI+PTSD had greater deficits in EFs than veterans with only TBI, specifically reduced processing speed and decreased inhibitory control. Four studies found that there was no additional effect on EFs with a co-occurring diagnosis as compared with TBI alone. The contradictory findings highlight the need for well-controlled research to better address this question.