Research suggests that military unit cohesion may protect against the development of post-traumatic stress disorder (PTSD). However, equivocal findings have led researchers to hypothesize a potential curvilinear interaction between unit cohesion and warzone stress. This hypothesis states that the protective effects of cohesion increase as warzone stress exposure intensifies from low to moderate levels, but at high levels of warzone stress exposure, cohesion loses its protective effects and is potentially detrimental. To test this theory, we conducted a test for curvilinear moderation using a sample of 705 Air Force medical personnel deployed as part of Operation Iraqi Freedom. Results did not support the curvilinear interaction hypothesis, although evidence of cohesion's protective effects was found, suggesting that unit cohesion protects against PTSD regardless of level of stress exposure.