This study aimed to determine the economic burden incurred from road traffic injuries in Thailand. It was designed as a prevalence-based cost-of-illness analysis from a societal perspective, employing a micro-costing bottom-up approach. It covered direct medical cost, direct non-medical cost, and indirect cost or productivity loss. Productivity loss covers the costs of work absence or death due to road traffic injuries suffered by persons of working age. We collected data on road traffic injuries and resource utilization which occurred in the fiscal year 2004. A simple random sampling was used to select 200 patients for analysis. The average cost of road traffic injuries per patient was USD 2,596 at 2004 prices. This can be divided into direct cost (USD 102, or 4%) and indirect cost (USD 2,494, or 96%). From these results, we can see that the indirect cost far outweighed the direct cost. To base decisions regarding road safety campaigns on savings of direct costs, particularly direct medical costs, is inadequate. Therefore, data on the complete cost of illness should be taken into account in the planning and creation of a road safety policy.