The Trauma Audit & Research Network (TARN) collects and audits major injury data from half of all trauma receiving hospitals in England and Wales. At the time of extraction for this analysis there were 183,550 cases on the database. Included patients reach hospital alive and subsequently either die as a result of injury, require intensive/high dependency care or interhospital transfer, or stay for more than 3 days. Our aim was to determine from an established trauma registry whether single injury AIS 4 codes in different body areas result in a similar threat to life. Patients with single injuries giving an Abbreviated Injury Scale score of 4 were selected from the TARN database. Mortality rates were calculated with 95% confidence intervals (CI) by body area. This cross tabulation also included the median age and Glasgow Coma Score (GCS). There is variation in the mortality rates by body region for single AIS 4 injuries with lower extremity and external injuries having a higher crude mortality rate. In multivariate analysis there is a significantly lower odds of death associated with AIS 4 single injuries in the head and thorax areas than in other body regions. Single AIS 4 injuries present a significantly greater threat to life dependant on the body region injured.