The Abbreviated Injury Scale (AIS) and the Injury Severity Score (ISS) are objective means of assessing injury. Accepted methodology involves retrospective scoring of injury based on discharge diagnoses. Recently, early clinical scoring, supplemented by review at discharge, has been introduced. A prospective study was instituted to compare these methodologies. Four hundred sixty consecutive victims of blunt trauma were scored using both clinical and retrospective methodologies by independent, blinded observers. Of these, 333 patients had a change in ISS, 174 with a change of greater than four points. The population mean ISS remained unchanged; however, paired values were significantly different (p less than .03). We conclude that either methodology is applicable for studies of large populations of trauma victims. When accurate individual AIS or ISS scoring is required, the clinical method combined with discharge review is most appropriate.