This study examined emotional and perceptional changes American people had experienced 10 to 12 months after the September 11 (9-11) terrorist attacks. A nationally representative sample of 807 U.S. adults ages 18 or older was interviewed using random-digit dialing that included unpublished numbers and new listings. The results indicated that 5 to 8% of the respondents had probable posttraumatic stress disorder symptoms such as angry outbursts, trouble falling asleep, difficulty concentrating, and experiencing nightmares even 10 to 12 months after the attacks. Twenty-two percent reported more frequent life-threatening perceptions and 50% more concerns about personal safety than before the 9-11 attacks. Chi-square and logistic regression analyses indicated that gender, age, race/ethnicity, geographic region, and employment status were significant predictors for experiencing differential emotional and perceptional changes. (Contains 3 tables.)