There has been speculation that post-traumatic stress disorder (PTSD) superimposed on mild traumatic brain injury (mTBI) may have synergistic, negative effects on cognitive functioning. The purpose of this study was to investigate differences in processing speed, executive functioning, and memory of 82 veterans with mTBI and PTSD, mTBI, and another psychiatric condition, or mTBI alone. It was hypothesized that there would be no group differences in cognitive performances. Participants completed the Trail Making Test, Stroop, Rey Complex Figure, and California Verbal Learning Test-2. There were no significant group differences on any cognitive measure. Findings suggest that PTSD and other psychiatric disorders do not necessarily have a negative exacerbating effect on processing speed, executive functioning, or memory in veterans with mTBI.