This study was designed as a preliminary investigation aimed at exploring variations in costs within a specific AIS category and to secondarily discuss the applicability of this type of cost analysis in assessing the ffectiveness of a mandatory restraint use law. Data from 1982 (the year prior to implementation of the Child Passenger Protection Act) and 1983 (the first year after implementation) were used. The data were obtained from a larger ongoing data collection effort in emergency rooms and the Coroner's Office in a large urban California county. Variation of costs within the minor injury category were found. The specific injury method of cost calculation was found to be more precise than use of an average AIS-1 cost. This study also demonstrated that costs associated with emergency room evaluation of those who are in fact uninjured must be included in cost analyses of a public policy measure, e.g. a mandatory restraint use law.