BACKGROUND: Air pollution has been associated with elevated blood pressure in adults. However, epidemiological evidence from children and adolescents is limited. We investigated the associations between long-term exposure to particulate matter (PM) air pollution and blood pressure in a large population of children and adolescents. METHODS: A cross-sectional analysis was performed in a nationally representative sample consisting of 43,745 children and adolescents aged 7 to 18years in seven provinces in China. Exposure to ambient fine particles (PM2.5) and thoracic particles (PM10) was estimated using spatiotemporal models based on satellite remote sensing, meteorological data and land use information. Mixed-effects (two-level) linear and logistic regression models were used to investigate the associations between PM exposure and systolic blood pressure (SBP), diastolic blood pressure (DBP) and hypertension. RESULTS: After adjustment for a wide range of covariates, every 10mug/m(3) increment in PM2.5 and PM10 concentration was associated with 1.46 [95% confidence interval (CI): 0.05, 2.88] and 1.36 (95% CI: 0.34, 2.39) mmHg increases in SBP, respectively. PM10 was also associated with higher prevalence of hypertension [odds ratio per 10mug/m(3) increment: 1.45 (95% CI: 1.07, 1.95)]. CONCLUSIONS: Long-term exposure to ambient PM air pollution was associated with increased blood pressure and higher prevalence of hypertension in children and adolescents. Our findings support air pollution reduction strategies as a prevention measure of childhood hypertension, a well-recognized risk factor of future cardiovascular health.