The purpose of the study is to determine if quetiapine is effective in the treatment of PTSD.

Objective: To assess the impact of quetiapine on core PTSD symptoms and associated psychiatric comorbidity including depressive and positive and negative psychotic symptoms.

Research Design: 12-week, double-blind, placebo-controlled, randomized, fixed-flexible dose trial of quetiapine monotherapy.

Intervention: Eligible patients will be randomized to receive quetiapine starting at 25 mg daily or matching placebo. Dose adjustments (to a minimum of 50 mg or a maximum of 800 mg), will be made at the investigator's discretion and according to patient's clinical response.

Inclusion Criteria:

• Male or female patients 18 years of age or older of any ethnic background meeting Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for PTSD.
• Score of at least 50 on the CAPS-SX at baseline.
• Competent to give informed consent.
• If female, patient should be using a medically approved contraceptive, or not otherwise be of childbearing potential.
• Patients who have not taken medications or herbal remedies for a psychiatric indication within one week prior to the randomized phase.
• Other medications, if any, must have been kept stable for at least one month prior to randomization.

Exclusion Criteria:

• History of sensitivity to quetiapine
• Use of antipsychotics, antidepressants, or benzodiazepines (except for short-term use during study as specified in Concomitant Medications section) within one week prior to randomization and throughout the study period.
• Medical conditions that may prevent safe administration of quetiapine including clinically significant hepatic, cardiac, or pulmonary disease.
• Medical disorders that may cause or exacerbate anxiety symptoms.
• Alcohol or drug abuse or dependence within one month of study entry as defined by DSM-IV criteria.
• Schizophrenia, schizoaffective disorder, or bipolar disorder.
• Suicidal or homicidal ideation or other clinically significant dangerousness
• Currently seeking compensation or increase in compensation for the effects of the trauma.
• Initiation or change in psychotherapy within 3 months of randomization.