Geocoding is the process of assigning latitude and longitude coordinates to data that contain spatial information. Geocoded records of motor vehicle collisions are an invaluable resource for injury prevention researchers. The objective of this study is to apply the postmile referencing system for geocoding collisions on Korean expressways and summarize the methodology and results with comparative research efforts in the USA. A street network provided by Korea Expressway Corporation was cleaned and calibrated using ArcGIS and a customized Visual Basic for Applications (VBA) tool. Geocoding via postmile referencing was determined to develop the most appropriate methodology for Korean expressways. A database of expressway collisions from 2003 to 2008 was geocoded, and 24,854 out of 24,879 (99.9%) collisions were successfully matched to the street network. This study established an effective methodology for geocoding collisions on Korean expressways. Future research will benefit from the development of a street network that can be updated over time to incorporate newly constructed roads. The methods for street network cleaning and error checking and the use of linear referencing to geocode collisions are easily transferable to highway networks in other countries. The geocoded database of expressway collisions can be used for numerous traffic safety improvement programs and help reduce fatalities.