Prospective studies of posttraumatic stress disorder (PTSD) in children that investigate simultaneously both cognitive and biological or psychophysiological predictors are rare. The present research reports on the impact of cognitive factors (trauma-related appraisals) and biological indicators (heart rate, morphine use) in predicting PTSD and depression symptoms following single-incident trauma. Children and adolescents (N= 48) were assessed within 4 weeks of an injury that led to hospital treatment and followed up 6-months later. While morphine did not predict initial PTSD severity, it was associated with lower levels of PTSD at follow-up. Reductions in PTSD symptoms (change scores) between assessments were similarly associated with morphine dosage. Trauma-related appraisals also contributed to PTSD and depression symptom severity. While slightly different patterns of results were obtained depending on whether static or change scores were examined, as a whole the study adds to a growing literature that morphine has the potential to reduce PTSD symptoms severity. Likewise the relationship between unhelpful trauma appraisals and posttrauma psychopathology was replicated.