The course of posttraumatic stress disorder (PTSD) in populations directly exposed to terrorist attacks is of major importance in the post-9/11 era. Because no systematic diagnostic studies of the most highly exposed individuals of the 9/11 terrorist attacks have yet been done, the Oklahoma City bombing remains a unique opportunity to examine PTSD over time in high-exposure terrorist victims. This study assessed 137 survivors in the direct path of the explosion at approximately 6 and 17 months postdisaster, using the Diagnostic Interview Schedule. Combined index and follow-up data yielded a higher (41%) incidence of PTSD than detected at index (32%) or follow-up (31%). All PTSD was chronic (89% unremitted at 17 months) with no delayed-onset cases. The avoidance and numbing symptom group C, unlike groups B and D alone, was pivotal to current PTSD status and was associated with indicators of functioning at index and follow-up. The findings at index were sustainable. This follow-up study confirmed the immediacy of onset of PTSD and its persistence over time, pointing to the need for early interventions that continue over the long term. Group C avoidance and numbing symptoms may aid in early recognition of PTSD and in predicting long-term functioning.