This report describes a 3-year follow-up study of survivors of a mass shooting incident. Acute-phase and 1-year follow-up data from this incident have been previously reported. The Diagnostic Interview Schedule/Disaster Supplement was used to assess 116 survivors at 1-2 months and again 1 and 3 years later, with an 85% reinterview rate. Examining the course of postdisaster posttraumatic stress disorder (PTSD) and major depression in individuals allowed detailed consideration of remissions and delayed detection of disorders not possible from data presenting overall rates across different time frames. Only about one half of the PTSD cases identified at any time over 3 years were in remission at the 3-year follow-up. Those who did not recover from PTSD diverged from those who recovered at 3 years by reporting increased numbers of symptoms over time, especially avoidance and numbing symptoms. Although women and people with preexisting disorders were at greater risk for the development of PTSD, these variables did not predict chronicity. Chronicity of PTSD was predicted by functional impairment and seeking mental health treatment at baseline. Chronicity of major depression was predicted by report of family history of depression and treatment for paternal alcohol problems. No delayed cases of PTSD were identified. Studies are needed to compare these characteristics of the course of PTSD with other populations, using consistent methodology to allow valid comparison.