This study assessed the relations between pretrauma risk (neuroticism, negative affect, prior distress) and protective (self-esteem, optimism) factors and posttraumatic stress disorder (PTSD) symptoms and potential mediators (subjective event-related distress, unsupportive social interactions, perceived control) of those relations. Students (N=1,528) at four U.S. universities completed online surveys assessing pretrauma risk and protective factors at Time 1 (T1); 84% (N=1,281) completed a survey 2 months later (T2). PTSD symptoms and the three potential mediators were assessed among those who experienced potentially traumatic events between T1 and T2 (n=264). PTSD symptoms related to prior traumas were controlled in all analyses. In structural equation modeling (SEM) analyses, the relation between risk factors and PTSD symptoms was mediated by unsupportive social interactions. Protective factors did not independently predict PTSD symptoms when risk factors also were included in the SEM models. Implications for research and practice are discussed.