We examine the association between trajectories of childhood adversities and Post-Traumatic Stress Disorder (PTSD) using a register-based Danish cohort. The DANish LIFE Course (DANLIFE) cohort includes and prospectively follows all individuals born in Denmark from 1980. We estimated the rate of PTSD diagnosed from age 16, according to childhood adversity trajectories from age 0 to 16 (n = 1 277 548). Trajectories were previously defined into 5 groups: Low Adversity, Early Life Material Deprivation, Persistent Material Deprivation, Loss or Threat of Loss, And High Adversity. We then estimated adjusted relative hazard ratios (aHR), and absolute hazards differences of PTSD according to childhood adversity trajectories in adjusted survival analysis. All analyses were stratified by sex. Individuals were followed for a median of 10·1 years a fter their 16th birthday, and 4966 individuals were diagnosed with PTSD. Compared with the low adversity group, children exposed to childhood adversity were more likely to be diagnosed with PTSD. The aHR for PTSD varied from 1·4 (95% CI: 1·3-1·5) in the Early Life Material Deprivation group, to 3·7 (3·3-4·1) in the High Adversity group, which corresponds to 8·3 extra cases of PTSD per 10 000 person years. The relative associations were comparable in men and women, but approximately twice as many women compared with men were affected. We report a clear association between exposure to childhood adversities and PTSD in young adulthood. The highest burden was among women in the high adversity group.