The recognition that current air pollution levels cause harmful health effects makes the definition of the air quality regulatory process imperative. This study examines the association between exposure to air pollution and hospital admissions in the city of São Paulo, aiming to support the development of measures to reduce such health risks. The authors conducted an ecological time series study of hospital admissions for respiratory and cardiovascular diseases in children and the elderly in relation to daily air pollution levels, using generalized additive Poisson regression models. All air pollutants except ozone showed a statistically significant association with admissions for respiratory and cardiovascular diseases. An increase of 10 microg/m3 in fine particulate matter was associated with a 4.6% increase in asthma admissions in children and a 4.3% increase in admissions for chronic obstructive pulmonary disease and 1.5% for ischemic heart disease in the elderly. These associations are consistent with a large body of literature in this area and indicate that the current air pollution levels in São Paulo have an important negative impact on the population's health.