This study looks at the health costs of particulate emissions from diesel-powered vehicles in Colombo City, Sri Lanka. Assessments were made of the make-up of the city's traffic and the potential health impact of various diesel emission sources. The financial cost of this pollution was then calculated using the Cost of Illnesses (COI) approach. It was found that particulate pollution (much of it coming from diesel vehicles) is linked to health problems that may be costing the city up to LKR22 billion per year. The study identified several pollution control options that would bring net benefits to the city. In other words, the cost of setting them up would be less than the health-related benefits they would deliver. In light of these findings, the study recommends that an effective vehicle inspection and maintenance program and an increase inroad user charges be considered priority projects for implementation.