Abstract Background Particulate matter with diameter less than 10 micrometers (PM 10 ) that originates from anthropogenic activities and natural sources may settle in the bronchi and cause adverse effects possibly via oxidative stress in susceptible individuals, such as asthmatic children. This study aimed to investigate the effect of outdoor PM 10 concentrations on childhood asthma admissions (CAA) in Athens, Greece. Methods Daily counts of CAA from the three Children's Hospitals within the greater Athens' area were obtained from the hospital records during a four-year period (2001-2004, n = 3602 children). Mean daily PM 10 concentrations recorded by the air pollution-monitoring network of the greater Athens area were also collected. The relationship between CAA and PM 10 concentrations was investigated using the Generalized Linear Models with Poisson distribution and logistic analysis. Results There was a statistically significant (95% CL) relationship between CAA and mean daily PM 10 concentrations on the day of exposure (+3.8% for 10 μg/m 3 increase in PM 10 concentrations), while a 1-day lag (+3.4% for 10 μg/m 3 increase in PM 10 concentrations) and a 4-day lag (+4.3% for 10 μg/m 3 increase in PM 10 concentrations) were observed for older asthmatic children (5-14 year-old). High mean daily PM 10 concentration (the highest 10%; >65.69 μg/m 3 ) doubled the risk of asthma exacerbations even in younger asthmatic children (0-4 year-old). Conclusions Our results provide evidence of the adverse effect of PM 10 on the rates of paediatric asthma exacerbations and hospital admissions. A four-day lag effect between PM 10 peak exposure and asthma admissions was also observed in the older age group.