Traumatic events are a particular type of stressor that may aect police ocers engaged in front line duties. In this study, speci®c types of social support predicted to buer the psychological and physical health eects of trauma are drawn from theory and empirical evidence in the area of post-traumatic stress. Social support, measured as the content of communication, and the ease of talking about trauma was tested with 527 working police ocers who responded to a questionnaire survey. Hierarchical regression analysis showed that the communication variables contributed to the variance in post-traumatic stress disorder and physical symptoms with dierential eects for dierent aspects of communication. Analysis of the eects of traumatic stress on symptoms for sub-groups at dierent levels of communication showed that some types of communication, such as the ease of talking about trauma or positive communications about work, moderate the eects of stress for police ocers, in that higher levels are associated with a weaker trauma±strain relationship. However, some types of communication buered stress only at moderate levels and other types may not be protective. These results are discussed in terms of the types and sources of social support that are likely to buer post-traumatic stress at work.