Smoking in hospitals is banned in most of European countries; nevertheless, implementing a total smoking ban is particularly difficult and policy breaches are frequent. Aim of our study was to monitor the compliance with the smoke-free policy within a hospital district by measuring particulate matters (PM2.5). We designed an observational study and identified six sensitive locations within the hospitals: surgical units, administrative offices, hall, outdoor main entrances and as controls an outdoor and an indoor area. To rule out potential confounders we included in the evaluation the roadways surrounding the hospital district. PM2.5 median concentrations observed in outdoor main entrances and in hall were significantly higher (16.4 and 13.4 µg m−3), as compared with the other settings (P < 0.0001). This data warrant an implementation of current policies to protect patients, visitors and employees from passive second-hand smoke leading to a smoking prohibition in any hospital surroundings.