Introduction: Brain infarction after trauma is uncommon. Injury of the carotid and vertebrobasilar arteries can cause brain infarction due to occlusion of brain blood flow. Case Presentation: Emergency medical service (EMS) brought a 4-year-old girl involved in a car accident to the emergency room. She had had seizure controlled by diazepam. She was unconscious and her Glasgow coma scale (GCS) score was eight. Early vital signs were stable. Her first brain CT scan showed a subdural hematoma (SDH). One day after admission to ICU, her GCS decreased to five; hence, a control brain CT was performed. The brain CT scan showed a brain infarction. Six days after admission, her status worsened and her GCS dropped to three and her pupils became dilated bilaterally and unresponsive to light; she was pronounced dead. Discussion: We present an uncommon case of posttraumatic brain infarction and synchronous SDH.