This paper examines risk factors for the development of Post Traumatic Stress Disorder (PTSD), and its severity and chronicity, in a group of 217 young adults who survived a shipping disaster in adolescence. The survivors were followed up 5 to 8 years after the disaster. Risk factors examined fell into three main categories: pre-disaster child and family vulnerability factors, including childhood psychopathology; objective and subjective disaster-related experiences; and post-disaster factors, including results from screening questionnaires administered 5 months post-disaster, coping mechanisms adopted subsequently, life events, and availability of social supports. Developing PTSD following the disaster was significantly associated with being female, with pre-disaster factors of learning and psychological difficulties in the child and violence in the home, with severity of exposure to the disaster, survivors' subjective appraisal of the experience, adjustment in the early post-disaster period, and life events and social supports subsequently. When all these factors were considered together, measures of the degree of exposure to the disaster and of subjective appraisal of life threat, and ratings of anxiety obtained 5 months post-disaster, best predicted whether survivors developed PTSD. For those survivors who developed PTSD, its duration and severity were best predicted not by objective and subjective disaster-related factors, but by pre-disaster vulnerability factors of social, physical, and psychological difficulties in childhood together with ratings of depression obtained 5 months post-disaster, and whether survivors received post-disaster support at school. The implications of these findings are considered for targeting assessment and intervention efforts at survivors most at risk of developing difficulties in adjustment following similar traumatic experiences.