BACKGROUND Women have been shown to be at higher risk than men of developing posttraumatic stress disorder (PTSD) after traumatic events. Women in New York City were more likely than men to have probable PTSD 5-8 weeks after the September 11, 2001, terrorist attacks on the World Trade Center. We explored the factors that could explain the higher prevalence of probable PTSD among women in the aftermath of the attacks. METHODS Data from a telephone survey of a randomly selected group of residents of Manhattan living south of 110th street, conducted 5-8 weeks after September 11, were used in these analyses. The survey assessed demographic information, lifetime experience of traumatic events, life stressors, social support, event exposure variables, perievent panic attacks, postevent concerns, and probable PTSD related to the attacks. We determined the contribution of key covariates that could explain the gender-probable PTSD relation through stratified analyses and manual stepwise logistic regression model building. RESULTS Among 988 respondents, women were two times more likely than men to report symptoms consistent with probable PTSD after the September 11 attacks. When adjusted for potential confounders, the association between gender and probable PTSD diminished from OR = 2.2 (95% confidence interval [CI] 1.3-3.6) to OR = 1.2 (95% CI 0.7-2.2). CONCLUSIONS These results suggest that specific behavioral and biographic factors (including previous traumatic experiences and psychological disorders, social responsibilities, and perievent emotional reactions) explained most of the excess burden of probable PTSD among women after a disaster. Isolating the characteristics that place women at greater risk for probable PTSD after disasters can inform public health prevention strategies and spur further research.