This paper presents an epidemiological study investigating the effects of long-term air pollution exposure on public health in Scotland, focusing on the 4 major urban areas, Aberdeen, Dundee, Edinburgh, and Glasgow.In particular, the associations between respiratory hospital admissions in 2005 and exposure to both PM10 and NO2 between 2002 and 2004 are estimated using a small-area ecological design.The implementation of such studies requires careful consideration of a number of statistical issues, including how to model spatial correlation, identifiability of the model parameters, and the possible effects of ecological bias.The results show that long-term exposures (over 3 years) to PM10 and NO2 are significantly associated with respiratory hospital admissions in Edinburgh and Glasgow, whereas the risks for Aberdeen and Dundee are generally positive but nonsignificant.