Virtual reality (VR) offers a new human-computer interaction paradigm in which users are no longer simply external observers of images on a computer screen but are active participants within a computer-generated three-dimensional virtual world. Posttraumatic stress disorder (PTSD) is a severe and often chronic and disabling anxiety disorder, which can develop following exposure to a traumatic event that involves actual or threatened injury to self or others. The term exposure therapy refers to several behavioral and cognitive behavioral treatment programs that involve confronting feared but safe thoughts, images, objects, situations, or activities in order to reduce pathological (unrealistic) fear, anxiety, and anxiety disorder symptoms. In the treatment of PTSD, exposure therapy usually involves prolonged, imaginal exposure to the patient's memory of the trauma and in vivo exposure to various reminders of the trauma. There is substantial evidence that exposure programs are highly effective in the treatment of PTSD. A Virtual Vietnam environment was created to explore the efficacy of VR Exposure therapy with Vietnam combat veterans with PTSD. Two virtual environments, a virtual Huey helicopter and a virtual clearing surrounded by jungle were created. Patients were exposed to their most traumatic Vietnam memories while immersed within the virtual environments following a standard treatment manual. Data are presented, and other applications of VR exposure therapy in the treatment of PTSD are discussed.