In this cross-sectional study, the authors examined the relationship between traffic-based air pollution and chronic, nonspecific respiratory symptoms among traffic policemen in Bangkok, Thailand. A total of 1,603 policemen who lived and worked in areas that had 3 different levels of airborne particulates were evaluated. The authors used a modified standardized questionnaire to identify nonspecific respiratory disease (NSRD) in participants. The prevalence of NSRD in heavily polluted, moderately polluted, and suburban areas was 13.0%, 10.9%, and 9.4%, respectively. Among nonsmokers, the age-adjusted prevalence of NSRD in the heavily polluted areas was significantly higher than in the suburban control area. Also among nonsmokers, the odds ratio for NSRD for each 10-microg/m3 increase in ambient particulate matter was 1.11. The authors concluded that the increased prevalence of respiratory symptoms among traffic policemen in Bangkok was associated with urban traffic air pollution.