Background: Secondhand smoke accounts for a considerable proportion of deaths due to tobacco smoke. Although the existing laws ban indoor smoking in public places in Sri Lanka, the level of compliance is unknown. Methods: Fine particulate matter (PM2.5) levels in 20 public places in Colombo, Sri Lanka were measured by a PM monitor (Model AM510-SIDEPAK Personal Aerosol Monitor). Different types of businesses (restaurants, bars, cafés, and entertainment venues) were selected by purposive sampling. Only the places where smoking was permitted were considered. Results: The average indoor PM2.5 ranged from 33 to 299μg/m3. The average outdoor PM2.5 ranged from 18 to 83μg/m3. The indoor to outdoor PM2.5 ratio ranged from 1.05 to 14.93. In all venues, indoor PM2.5 levels were higher than the Sri Lankan ambient PM2.5 standard of 50μg/m3. All indoor locations had higher PM2.5 levels as compared to their immediate outdoor surroundings. Conclusion: The study highlights the importance of improving ventilation and enforcing laws to stop smoking in public places. © 2012 Wiley Periodicals, Inc.