Oklahoma City bombing survivors (N = 182) were studied 6 months post-bombing and reassessed approximately 1 year later (N = 141) to determine the longitudinal course of post-traumatic stress disorder (PTSD) and other psychiatric disorders. The Diagnostic Interview Schedule assessed lifetime, current, predisaster, and post-bombing psychiatric diagnoses at both assessment points. One-third of the Oklahoma City bombing survivors had PTSD at index, and similar rates were diagnosed at follow-up. More recovery from depression was apparent than from PTSD. No delayed onset PTSD was observed, and all PTSD was chronic. Avoidance and numbing symptoms were dominant in defining the development of PTSD. Early onset and chronicity of PTSD indicate need for prompt and long-term intervention after disasters. Focus on avoidance and numbing symptoms may aid in identification of individuals needing intervention and monitoring the course of PTSD.