 Posttraumatic Stress Disorder, a common mental disorder among Veterans, is marked by painful re-experiencing of a traumatic event, often together with depression, fearfulness, and social isolation. Despite major advances in rehabilitation, many Veterans continue to be disabled by PTSD. One possible new approach involves the use of shelter dogs, which might relieve symptoms and aid reintegration into society by providing emotional support and a greater sense of security. In this randomized controlled trial of 48 Veterans with chronic PTSD, we will evaluate whether the half who adopt a dog from the San Antonio Humane Society show greater improvement in their PTSD symptoms over the first three months than the half who are assigned to a waiting list. 