Two inter-related studies examined the effect of the September 11, 2001, terrorist attacks on attitudes towards war and violence. A three-wave between-subjects analysis revealed that attitudes towards war became more positive after September 11, 2001 and remained high over a year afterwards. Self-reported trait physical aggression also rose after September 11. Attitudes towards penal code violence (PCV) became more positive immediately after September 11, but were somewhat reduced a year afterward. A two-wave within subjects study revealed that war attitudes became even more positive at 2 months post-September 11. Attitudes towards PCV became less positive during this time period, but only for women. Other aggression-related attitudes were not affected in either study. These studies demonstrate that a large-scale event can change attitudes, but those attitudes must be directly relevant to the event.