No prior studies exist in Mainland China examining the association of outdoor air pollution with hospital admissions. In this study, we conducted a time-series analysis to examine the association of outdoor air pollutants (PM10, SO2, and NO2) with both total and cause-specific hospital admission in Shanghai, using three years of daily data (2005-2007). Hospital admission and air pollution data were collected from the Shanghai Health Insurance Bureau and Shanghai Environmental Monitoring Center. Natural spline model was used to analyze the data. We found outdoor air pollution was associated with increased risk of total and cardiovascular hospital admission in Shanghai. The effect estimates of air pollutants varied by lag (L) structures of pollutants' concentrations. For lag 5, a 10 mu g/m(3) increase in concentration of PM10, SO2 and NO2 corresponded to 0.18% (95% CI: -0.15%, 0.52%), 0.63% (95% CI: 0.03%, 1.23%), and 0.99% (95% CI: 0.10%, 1.88%) increase of total hospital admission; and 0.23% (95% CI: -0.03%, 0.48%), 0.65%(95% CI: 0.19%, 1.12%), and 0.80% (95% CI: 0.10%. 1.49%) increase of cardiovascular hospital admission. The associations appeared to be more evident in the cool season (from November to April) than in the warm season (from May to October). We found significant effects of gaseous pollutants (SO2 and NO2) after adjustment for PM10. Our analyses provide the first evidence in China that the current air pollution level has an effect on hospital admission and strengthen the rationale for further limiting air pollution levels in Shanghai. (C) 2010 Elsevier B.V. All rights reserved.