High levels of major outdoor air pollutants have been documented in Lebanon, but their health effects remain unknown. The Beirut Air Pollution and Health Effects study aimed to determine the relationship between short-term variations in ambient concentrations of particulate matter (PM10 and PM2.5) and emergency hospital admissions in the city of Beirut, and whether susceptible groups are more greatly affected. An autoregressive Poisson model was used to evaluate the association between daily concentrations of particulate matter and respiratory and cardiovascular emergency hospital admissions after controlling for confounders. All variables were measured during 1 year from January 2012 to December 2012. Relative risks of admissions for respiratory and cardiovascular diseases were calculated for an increase in 10 μg.m(-3) of pollutant concentrations. Total respiratory admissions were significantly associated with the levels of PM10 (1.012 [95% CI 1.004-1.02]) per 10 μg.m(-3) rise in daily mean pollutant concentration for PM10 and 1.016 [95% CI 1.000-1.032] for PM2.5 on the same day. With regard to susceptible groups, total respiratory admissions were associated with PM2.5 and PM10 within the same day in children (relative risk (RR), 1.013 and 1.014; 95% confidence interval, 0.985-1.042 and 1.000-1.029 for PM2.5 and PM10, respectively). Moreover, a nearly significant association was found between particles and total circulatory admissions for adults and elderly groups in the same day. These results are similar to other international studies. Therefore, air pollution control is expected to reduce the number of admissions of these diseases in Lebanon.