We examine prospectively the influence of two separate but potentially inter-related factors in the etiology of post-traumatic stress disorder (PTSD): childhood maltreatment as conferring a susceptibility to the PTSD response to adult trauma and juvenile disorders as precursors of adult PTSD.The Dunedin Multidisciplinary Health and Development Study (DMHDS) is a birth cohort (n = 1037) from the general population of New Zealand's South Island, with multiple assessments up to age 38 years. DSM-IV PTSD was assessed among participants exposed to trauma at ages 26-38. Complete data were available on 928 participants.Severe maltreatment in the first decade of life, experienced by 8.5% of the sample, was associated significantly with the risk of PTSD among those exposed to adult trauma [odds ratio (OR) 2.64, 95% confidence interval (CI) 1.16-6.01], compared to no maltreatment. Moderate maltreatment, experienced by 27.2%, was not associated significantly with that risk (OR 1.55, 95% CI 0.85-2.85). However, the two estimates did not differ significantly from one another. Juvenile disorders (ages 11-15), experienced by 35% of the sample, independent of childhood maltreatment, were associated significantly with the risk of PTSD response to adult trauma (OR 2.35, 95% CI 1.32-4.18).Severe maltreatment is associated with risk of PTSD response to adult trauma, compared to no maltreatment, and juvenile disorders, independent of earlier maltreatment, are associated with that risk. The role of moderate maltreatment remains unresolved. Larger longitudinal studies are needed to assess the impact of moderate maltreatment, experienced by the majority of adult trauma victims with a history of maltreatment.