This study assesses the psychological consequences of participation in a mental health study among people recently exposed to the September 11 attacks. Using cross-sectional telephone surveys, we interviewed random samples of English-speaking or Spanish-speaking adults living in New York City during the attacks 1 year after this event. Altogether, 2,368 people completed the surveys, including a random sample of 1,173 respondents who received mental health services after the attacks. Results indicated that 15% of New Yorkers found some of the survey questions stressful, whereas 28% of those who sought treatment found this to be the case. However, less than 2% reported being upset at survey completion, and among these persons, only four people consented to speak to the study's mental health consultant. Although the majority of those expressing adverse reactions had sought postdisaster treatment, even among these subjects, only 3% were still upset at survey completion, and 2% wanted more information about counseling services. In addition, more than 70% of participants expressed positive sentiments about survey participation. Predictive models indicated that respondents who met study criteria for posttraumatic stress disorder, depression, or anxiety were more likely to find questions stressful, with people having posttraumatic stress disorder or depression the most likely to be upset and to consent to psychiatric consultation at completion. We suggest that, with the proper safeguards, research with persons exposed to a resent mass urban disaster generally can be conducted safely and effectively.