Characteristic patterns of injury to children in automobile crashes resulting from lap and lap-shoulder belts have been described for many years. These injuries are known as the "seat belt syndrome." We present a typical case of seat belt syndrome involving a 4-year-old boy and review the current literature on the topic, highlighting proposed mechanisms of intra-abdominal and spine injuries. In addition, recent research findings identifying a new pattern of injuries associated with inappropriate seat belt use in young children are reviewed. Emergency physicians must consider these seat belt-related injuries in the initial evaluation of any child involved in a motor vehicle crash who was restrained with the vehicle seat belt.