This study examined the impact of the September 11 terrorist attacks on graduate and undergraduate students and the role of optimism in posttraumatic distress. A sample of 457 students who attended courses at three schools of social work (Nevada, Pennsylvania, and Washington) participated in the study. A quarter of them had a known person as an immediate victim of the attacks. Multivariate analysis showed that posttraumatic stress disorder symptom scores were positively related to personal loss and two types of previous trauma reactivated by the attacks, and levels of initial negative emotional response. Optimism and its interaction with personal loss were inversely associated with posttraumatic stress disorder symptom scores. (Contains 1 table.)