Subjects were 46 participants who comprised a subset of a population based sample (n=109) evaluated at the Mount Sinai School of Medicine (MSSM) four to six years following the 9/11 attacks (Yehuda et al., 2009). The subjects studied at the MSSM were those who responded positively to a mailing asking participants to have an in-person diagnostic evaluation, complete self-report questionnaires and permit an 8 am blood draw. The study was approved by the Institutional Review Board (IRB) at the Mount Sinai School of Medicine; all subjects provided written informed consent and were subsequently screened to establish eligibility. Subjects were excluded if they met criteria for primary psychotic disorder, bipolar illness, alcohol or substance dependence, or major endocrine, neurological, or other medical illness, including diabetes. Although subjects with PTSD showed greater number of lifetime psychiatric diagnoses than those without PTSD (Table 1), as has been previously described (Breslau et al. 2000), none were receiving psychiatric treatment or taking psychotropic medications at the time of participation. The 46 subjects included in this report were those with remaining frozen samples available for endocannabinoid assay who had previously provided consent for analyses of compounds unrelated to the goals of the initial investigation, i.e., associations with genotype. Selection was based purely on availability of biological sample in conjunction with appropriate consent, and not on any other inclusion or exclusion criteria, clinical or otherwise. Subjects with endocannabinoid determinations (n=46) were similar in age, gender distribution, and lifetime trauma exposure histories to the remaining members of the original cohort (n=63). Of 46 subjects, 22 were deemed to have suffered direct, high magnitude exposure to the events of 9/11 (direct exposure to the events of 9/11), whereas 24 reported indirect exposure. ‘Direct exposure’ was assigned to participants who were in the vicinity of the World Trade Towers at the time of the attacks with immediate threat to their safety or survival, or had suffered the loss of family members or intimate friends on 9/11. ‘Indirect exposure’ was attributed to those who witnessed collapse of the Towers from a safe distance, were informed of the attacks while out of town, or observed the events on TV, without enduring direct threat to self or family members.