Smoking in hospitals is banned in many European countries; nevertheless, the level of compliance is diverse, and, in some cases, smoking areas remain. The present study describes the levels of second-hand smoke, as derived from respirable suspended particle measurements, in a sample of European hospitals during the year 2007. The present study was a multicentric descriptive cross-sectional study carried out in 30 hospitals in seven European countries (Austria, Belgium, France, Germany, Greece, Romania and Spain). Particulate matter with a 50% cut-off aerodynamic diameter of 2.5 microm (PM(2.5)) concentration was measured by means of a hand-held laser-operated monitor of particle size and mass concentration in six selected indoor locations. Medians and interquartile ranges of PM(2.5) concentration were computed in order to describe the data by country and location of measurement. The median PM(2.5) concentration in all countries and locations was 3.0 microg x m(-3), with half of the measurements ranging 2.0-7.0 microg. x m(-3). PM(2.5) levels were similar across countries. Eleven (5.5%) measurements were >25.0 microg x m(-3), which is the 24-h mean limit recommended by the World Health Organization outdoor air quality guideline. The present results show that exposure to second-hand smoke in this sample of European hospitals is very low, and can be easily monitored in order to ensure smoke-free legislation compliance.