Current available evidence suggests that air pollution, especially particulate matter <10 mum in aerodynamic diameter (PM10), has acute and chronic effects on health. We aimed to evaluate the epidemiological association between 24-h PM10 levels and acute coronary syndrome (ACS). We analyzed the number of daily admissions at the emergency unit (ED) of patients with suspected ACS, and the number of daily diagnosis of ACS in the same local ED according to the 24-h PM10, over a nearly 3-month period. 209 out of the 1,688 patients admitted to the ED with a clinical suspicion of ACS had a definitive diagnosis of ACS. Whereas the mean number of ED admissions for suspected ACS did not differ significantly according to the 24-h levels of PM10 (18 +/- 1 vs. 17 +/- 1; P = 0.13), the mean number of diagnoses of ACS was 26% higher when the 24-h levels of PM10 were >50 microg/m(3) (2.4 +/- 0.2 vs. 1.9 +/- 0.2; P = 0.03). A statistically significant association was also observed between 24-h PM10 levels and daily number of ACS diagnoses (r = 0.26; P < 0.001), but not between 24-h PM10 levels and daily ED accesses for suspected ACS (r = 0.12; P = 0.24). Taken together, these results support the existence of an epidemiologic association between air pollution and acute cardiovascular events.