The New Injury Severity Score (NISS) is a tool developed to easily assess the injury severity for a trauma patient. This review analysed how well the NISS predicts in-hospital mortality for trauma patients by assessment of 11 observational studies. NISS was found to be a good overall predictor of in-hospital mortality in blunt as well as penetrating trauma cases. However, additional high-quality studies are required in order to draw definite conclusions in a Scandinavian hospital setting and patient population.