For the 1993 calendar year the National Highway Traffic Safety Administration (NHTSA) National Accident Sampling System (NASS) used AAAM's Abbreviated Injury Scale, 1990 Revision (AIS90) to code motor vehicle injury severity. Between 1987 and 1992, NASS used the AIS 1985 Revision (AIS85) to code injury severity. The 1990 revision of AIS resulted in substantial changes in the way injuries are coded compared with AIS85 with the result that AIS90 has a higher proportion of injuries in less severe categories than the AIS85 version. This paper presents a severity conversion method in which NASS 1993 and later injury codes are assigned AIS85 severities. Because of the substantial differences between AIS85 and AIS90, researchers are cautioned against combining data from these two coding systems without first applying the conversion.