This study used structural equation modeling (SEM) to evaluate the relative strength of associations between combat exposure, four posttraumatic stress disorder (PTSD) symptom factors, and functional impairment as indexed by Global Assessment of Functioning (GAF) scores in a sample of 315 veterans assessed at a Department of Veterans Affairs PTSD clinic. Results showed that the association between combat exposure and GAF scores was fully mediated by PTSD severity. The best-fitting model included direct paths from combat exposure to reexperiencing symptoms and from avoidance and numbing symptoms to GAF. However, only 17% of variance in GAF was accounted for by PTSD. The results raise concern about the use of the GAF score as a benchmark for quantifying combat PTSD-related functional impairment.