Abstract: A cardinal feature of posttraumatic stress disorder (PTSD) is decreased sleep quality. Anxiety sensitivity (AS) is one factor that has shown early theoretical and empirical promise in better understanding the relation between sleep quality and PTSD outcomes. The current study is the first to test the independent and interactive effects of sleep quality and AS on PTSD symptoms. Consistent with hypotheses, AS and sleep quality were found to be independent and interactive predictors of PTSD symptom severity in our sample of male military veterans seeking treatment for PTSD. Slope analyses revealed that AS was differentially related to PTSD symptom severity as a function of quality of sleep. The veterans with good sleep quality and relatively lower levels of AS had the lowest level of PTSD symptoms, whereas the veterans with poor sleep quality and low AS evidenced severity of PTSD symptoms similar to those with high AS.