Traumatic childhood events are some of the few identifiable and to some extent preventable causes of psychiatric illness. Children exposed to severely stressful events may react with post-traumatic stress disorder (PTSD) and this may impact their level of function in daily life, their future development and mental health. The traumatic stress model suggests that traumatic stress in the family, community violence, and other traumas are regarded as additive environmental factors that can outweigh protective compensatory factors and thus interact with individual vulnerabilities. This study is based on prospective panel data including the whole population of children born in Denmark from 1984 to 1994, who are followed from age 7 to age 18 (N = 679,000) in the window between 2001 and 2012. Risk factors for first-time diagnose with PTSD are analyzed by the discrete time log-odd model. We found a lifetime prevalence of 2.3% PTSD in school-age children (n = 15,636). In accordance with the model, indicators of traumatic stress in the family, family disintegration, community violence, and individual vulnerabilities predicted later diagnose with PTSD. Individual neurodevelopmental disorder – especially autism (adjusted Odds Ratio (OR 7.1) and ADHD (OR 10.7) – were predicative of PTSD. The results cooperated the traumatic stress model. Some results were inconsistent with the traumatic stress model e.g., parental substance abuse were associated with less than expected PTSD in school-age children when adjusted for other risk factors. This indicates that PTSD may be underestimated in these groups. PTSD diagnoses in administrative records underestimate the prevalence, systematically. Efforts to increase PTSD screening may allow for better management.