A Modified Injury Severity Scale (MISS) was devised to classify 110 pediatric patients with multiple trauma. Each of five body areas (neurologic, face and neck, chest, abdomen and pelvic contents, and extremities and pelvic girdle) were ranked by severity according to the carefully-defined categories of the AMA Abbreviated Injury Scale (AIS), with minor modifications. The AIS grades of injury are: 1—mild; 2—moderate; 3—severe, not life-threatening; 4—severe, life-threatening, survival probable, and; 5—critical, survival uncertain. The MISS score is defined as the sum of the squares of the three most-severely injured body areas. Final patient outcomes were ranked as: normal; disabled (some limitation not previously present); dependent (for some activity of daily living), and death. Overall mortality was 14.5% with 9% disability and 0.9% dependency. Both mortality and morbidity correlated linearly with increasing MISS score. Of patients with MISS scores >25, 60% died and 16.7% were either disabled or dependent, while no mortalities and 2.5% disabilities were seen with scores <25. All patients with Injury Severity Scale (ISS) scores ≥40 died. Neurologic injuries were present in 73% of patients, with 58% having this as the most severly injured area. All fatalities and disabilities had some degree of neurologic injury, although 12.5% of fatalities and 20% of disabilities were non-neurologic in nature. All patients with neurologic severity grade of 5 either died or were disabled or dependent, while disability fell to 40% with grade 4, 3.9% with grade 3, and 0% with grades 1 or 2 neurologic injury. The modified ISS is a simple, accurate predictor of both morbidity and mortality in pediatric trauma. The best predictors of mortality and morbidity were MISS score ≥25 and the degree of neurologic injury [Glasgow Coma Scale (GSC)<9].