The cumulative effects of trauma were examined in 108 workers at the site of a major air disaster at 4 time points over a year following the crash. The influence of trauma history on chronic distress and physiological arousal associated with the crash were examined. Stress levels were expected to differ on the basis of the similarity of prior trauma exposure to work at the crash site. Prior traumatic exposure that was "dissimilar" to this type of work was associated with greater vulnerability to crash-related stress, that is, more distress and crash-related intrusions during the year following the crash. Accumulation of a variety of different traumatic experiences appeared to sensitize workers to the new stressor and to perpetuate chronic stress. Understanding the role of trauma history is important for improving intervention efforts aimed at alleviating stress following a trauma.