This study examined prospectively the role of parental psychopathology among other predictors in the development and persistence of posttraumatic stress disorder (PTSD) in 57 hospitalized youths aged 7–18 years immediately after a road traffic accident and 1 and 6 months later. Self report questionnaires and semistructured diagnostic interviews were used in all 3 assessments. Neuroendocrine evaluation was performed at the initial assessment. Maternal PTSD symptomatology predicted the development of children's PTSD 1 month after the event, OR = 6.99, 95% CI [1.049, 45.725]; the persistence of PTSD 6 months later was predicted by the child's increased evening salivary cortisol concentrations within 24 hours of the accident, OR = 1.006, 95% CI [1.001, 1.011]. Evaluation of both biological and psychosocial predictors that increase the risk for later development and maintenance of PTSD is important for appropriate early prevention and treatment.