Background: Posttraumatic stress disorder (PTSD) is a prevalent disorder that has been associated with elevated rates of medically unexplained physical symptoms, significant functional impairment, and high health care use. However, little is known about actual health care costs associated with PTSD. Methods: We administered the PTSD Checklist (PCL) to 1225 female members of a metropolitan health maintenance organization and validated the instrument using a structured PTSD interview in a subset of 268 women. Participants were classified into 3 groups by PCL score: low (< 30), moderate (30-44), and high (greater than or equal to 45). By using the cost accounting system of the health maintenance organization, we examined differences between the groups with respect to total and component health care costs, controlling for chronic medical illness and other forms of psychological distress. Results: The total unadjusted mean +/- SD annual health care costs were $3060 +/- $6381 (median, $1283) for the high PCL score group, $1779 +/- $3008 (median, $829) for the moderate PCL score group, and $1646 +/- $5156 (me-dian, $609) for the low PCL score group. After adjusting for depression, chronic medical disease, and demographic factors, women with high PCL scores had a significantly greater odds of having nonzero health care costs compared with women with low PCL scores (odds ratio, 13.14; 95% confidence interval, 1.70-101.19). Compared with women in the low PCL score group, those in the moderate PCL score group had, on average, a 38% increase in adjusted total annual median costs, and those in the high PCL score group had a 104% increase. Conclusions: Women with PTSD symptoms in this study had significantly higher total and component health care costs, even after controlling for depression, chronic medical illness, and demographic differences. These findings are similar to those found in studies of costs related to major depression and suggest that instituting health services interventions to improve recognition and treatment of PTSD in primary and specialty care clinics may be a cost-effective approach for lowering the prevalence of this disorder.