The authors conducted confirmatory factor analyses to test three-factor and four-factor models of posttraumatic stress disorder (PTSD) using the PTSD Checklist with college students reporting a traumatic event history. The authors found support for the three-factor "DSM-IV"-based PTSD diagnostic model including reexperiencing, avoidance/numbing, and hyperarousal symptom factors, with slightly better support for a four-factor model separating the avoidance and numbing factors. Results further attest to the PTSD Checklist's construct validity, and to research finding that PTSD avoidance and numbing constructs are distinct. (Contains 1 figure.)