The purpose of this study is to compare two kinds of therapy for Posttraumatic Stress Disorder (PTSD): exposure therapy (ET) and Interpersonal Psychotherapy (IPT). The results of this study will allow us to see if IPT and ET are equally effective in treating PTSD due to Military Sexual Trauma, with the long-term goal of making PTSD treatment effective for as many people as possible.

Inclusion Criteria:

• English-speaking
• Military Sexual Trauma (MST) survivors, with MST defined as actual or threatened sexual violence, from Vietnam era to current Operation Iraqi Freedom/Operation Enduring Freedom/Operation New Dawn
• Diagnosed with PTSD consequent to MST, with a minimum CAPS score > 40
• Medically stable at time of study enrollment (for persons with chronic injuries and that any disability present does not prevent attendance of weekly outpatient therapy sessions)
• Ability to provide informed consent and function at an intellectual level sufficient to allow accurate completion of all assessment instruments
• Stable on psychotropic medication for the prior 60 days

Exclusion Criteria:

• Lifetime or current diagnosis of schizophrenia or other psychotic disorder, bipolar disorder
• Participation in a clinical trial or concurrent evidence-based treatment for MST-related psychiatric conditions or PTSD during the previous 3 months
• Current evidence of significant unstable medical illness or organic brain impairment such that the patient could not attend sessions regularly or complete assessments
• Patients who in the investigator's judgment pose a current homicidal or suicidal risk
• Current or history of substance dependence in the past 90 days.