The authors have examined data from the National Accident Sampling System (NASS) to determine the factors in the crash which increase the severity of harm to the occupant. This paper describes the results to date. The mean speed for rollovers is found to be much higher than for planer crashes. Vehicle speed is an important predictor of injury outcome. However, imprecision in coding the speed and the vehicle damage detract from the ability to use these variables for injury prediction. Data collection improvements are suggested.