Accurate information about injuries and their causes is essential to road safety research, policy development and evaluation. Such information is most powerful when it is available for all road crashes within a jurisdiction. The Western Australian Road Injury Database achieves this through the on-going linkage of crash details from reports to police with the details of injuries to casualties contained in hospital and death records. Over the 10-year period 1987-1996, 386,132 road crashes involving 142,308 casualties were reported to the police in Western Australia. There were also 47,757 hospital discharge records and 2,906 death records related to road crashes during this period. Of the 142,308 police casualties, 17 848 had a matching hospital discharge record and 2,454 had a matching death registration. Linkage within the hospital records revealed that the 47,757 discharge records involved 43,179 individuals, of whom 39,073 were admitted to hospital once, 3,653 were admitted twice, 374 were admitted three times and 78 were admitted more than three times. Of the 43,179 hospitalised casualties, 817 had a matching death record. Linked police, hospital and death records of road crash casualties provide accurate outcome information for casualties in crashes reported to the police. In addition, estimates of under reporting of crashes for different road user groups can be made by comparing hospital records with and without a matching police record. This article demonstrates the power of a linked system to answer complex research questions related to outcome and under-reporting.