This study is exploring the use of an intervention designed to treat PTSD in individuals with comorbid PTSD and substance abuse resulting from the attacks of September 11 or from military service in Iraq. A cognitive behavioral treatment protocol will be used to treat PTSD. The exposure component of the protocol will be enhanced with the use of virtual reality in which the client will view a virtual environment while describing their trauma.

Inclusion Criteria:

• English-speaking
• Between the ages of 18 and 70
• Exposed to the WTC Attacks (were in towers or in the immediate area) or veterans of the Iraq War
• Diagnosed with PTSD symptoms
• Current substance abuse disorder or history of substance abuse disorder

Exclusion Criteria:

• Presence of current organic mental disorder
• Presence or history of schizophrenia, bipolar disorder or depression with psychotic features, delusional disorder
• Active suicidal ideation, intent, or plan
• Active homicidal ideation, intent, or plan
• Use of pacemaker
• Medically unstable
• History of seizures