Although exposure to a traumatic event is thought to be the main aetiological factor in the development of post-traumatic stress disorder, there remain large unexplained individual differences in the severity and chronicity of symptoms. The aim of the present study was to assess the relative contribution of a number of social and psychological factors which are thought to determine symptoms. Crisis support and life-events subsequent to the disaster are the two best predictors of general psychological well-being, whereas a sense of helplessness during the disaster and bereavement are the two best predictors of intrusive symptomatology.