The article is a bibliographic review which intends to present the actual range of researches comparing the Injury Severity Score (ISS) and the New Injury Severity Score (NISS). Databases were searched using the keyword NISS, with 42 articles, 23 of which didn't compare the two indexes. Most part of the 19 selected articles showed that NISS has been more accurate in predicting the outcomes (dependent variables) than ISS, moreover in severe and specific trauma. Studies with populations between 1,000 and 10,000 resulted in NISS-favorable results, whereas studies with populations larger than 10,000 or smaller than 1,000 showed either NISS-favorable results or no difference between the two groups. However, there were no studies showing ISS-favorable results. These results and the easier calculation of NISS lead to a future replacement of ISS by NISS.