Abstract: Objective: The heightened prevalence rates of respiratory problems and posttraumatic stress disorder (PTSD) among New York area residents following the World Trade Center disaster on September 11, 2001, have received national attention. Although there is some evidence suggesting that PTSD is associated with increased risk for asthma, this relationship has not been well documented in this population at high risk for both disorders. There is also a need to examine this relationship while controlling for notable confounds, including dust exposure and smoking.Method: This study examined the association between symptoms indicative of probable PTSD and the diagnosis of asthma following 9/11 among the individuals who participated in the World Trade Center Health Registry (WTCHR) baseline study between September 2003 and November 2004. A total of 71,437 participants enrolled in this study and completed questionnaires pertaining to exposure, physical health symptoms before and after 9/11, and self-reported PTSD symptoms.Results: Logistic regression revealed that, compared to participants without probable PTSD, individuals with probable PTSD were 1.65 times more likely to be diagnosed with asthma following 9/11, which was significant after controlling for the effects of gender, ethnicity, income, smoking status, dust exposure, and nonspecific psychological distress [Wald χ2 (1)=52.375, P<.001].Conclusion: These results suggest that PTSD symptoms are associated with the development of asthma following 9/11 and that this relationship is not explained by sociodemographic, environmental, and lifestyle factors.