This study seeks to examine the efficacy of hydrocortisone administration in the augmentation of the therapeutic effects of Prolonged Exposure (PE) therapy, an empirically tested treatment shown to be effective in the the treatment of posttraumatic stress disorder (PTSD). The augmentation builds on both the translation of neuroscience findings demonstrating the effects of glucocorticoids (GCs) on learning, and on empirical clinical findings from other investigators demonstrating beneficial effects of GCs in reducing traumatic memories in trauma-exposed persons.

Inclusion Criteria:

• A primary diagnosis of chronic PTSD according to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnostic criteria, resulting from a deployment-related traumatic event, and a minimum PTSD severity of 50 (CAPS).
• The veteran must either be unmedicated or on a stable psychotropic regimen (i.e., 1 or more months on the same regimen).

Exclusion Criteria:

• Lifetime history of psychotic disorder, bipolar disorder, or obsessive compulsive disorder.
• Moderate or severe traumatic brain injury (TBI).
• A medical or mental health problem other than PTSD that requires immediate clinical attention.
• Substance abuse or dependence within the last 3 months.
• Suicidal risk (as determined by response of 5 or 6 on the suicidality items of the Montgomery Asberg Depression Rating Scale (MADRS)) and/or assessed suicide risk on the basis of clinical judgment.
• Persons on a psychotropic medication regimen that has not been consistent for one month.
• Presence of diabetes mellitus or any current unstable medical illness or condition that represents a contraindication to taking glucocorticoids (this will be determined by history and/or abnormal laboratory findings at medical clearance).
• Unwillingness to discontinue other specialized psychotherapy for PTSD during the 10 weeks of study treatment and the 6 week follow-up. (Self-help (non-trauma focused) groups or supportive counseling can be continued but not initiated.)
• Pregnant women or those planning to become pregnant within the study period will not be enrolled. Female participants must agree to use an effective method of birth control (i.e., oral contraceptive, Norplant, diaphragm, condom, or spermicide, abstinence) during the course of the study to ensure they do not become pregnant during the course of the study.