The chronicity and morbidity of established post-traumatic stress disorder (PTSD) has stimulated interest in recognizing and understanding the early development of the disorder. Acute stress disorder, a new diagnosis intended to facilitate early case detection, rests on the occurrence of dissociative reactions. It remains uncertain whether dissociation is a universal or unique early predictor of subsequent PTSD. Traumatic injury is an important and relatively understudied antecedent of PTSD. The objective of this study was to preliminarily identify which previously implicated early reactions and risk factors would apply to the prediction of PTSD following severe traumatic injury. Patients admitted to a regional Level I trauma center following life threatening events who had recall of the incident and did not have signs of traumatic brain injury or recent psychopathology were enrolled. Comprehensive assessments were conducted during hospitalization and after discharge approximately 2 months after the traumatic event. At follow-up, 24% of the available 50 subjects met full criteria for PTSD and an additional 22% met criteria for two of three symptom clusters. Early symptoms of heightened arousal and coping with disengagement were independent predictors of PTSD severity at follow-up. Relationships to initial dissociative reactions and a diagnosis of ASD were not significant. These early predictors found in a setting of severe injury only partially overlap findings from previous PTSD studies.