We hypothesize that apnea induced by shaking or by shaking combined with impact plays a major role in the pathophysiology of nonaccidental head trauma and accounts for the poor outcome in this subgroup of patients. In a retrospective study of 28 children who suffered significant nonaccidental head injury, 57% had a history of apnea prior to hospitalization, 82% were intubated upon admission, and 71% had early seizures. For further evidence of ischemia and hypoxia, the first recorded blood pressure was < 80 in 50% and the arterial pH < 7.3 in 54%. Seventy-one percent had diffuse brain swelling which is characteristic of cerebral hypoxia and/or ischemia on the first CT scan. None of the children who had clinical evidence of cerebral hypoxia or ischemia had a good outcome. We conclude that trauma-induced apnea causes cerebral hypoxia and/or ischemia which is more fundamental to outcome than the mechanism of injury (shaken vs. shaken with impact), subdural hemorrhage, subarachnoid hemorrhage, diffuse axonal injury, parenchymal shear, or brain contusion.