The authors conducted a cross-sectional comparative prevalence study to evaluate the effect of pollution on individuals who lived in an industrial zone in Sri Lanka. In this study, 81 male and female children who were 1-12 yr of age and 158 adults (51 males, 107 females) in the industrial zone were matched with 73 children (32 males, 41 females) and 146 adults (58 males, 88 females), respectively, who lived in a nonindustrialized area and whose ages were similar to those of the exposed individuals. The authors used a pretested questionnaire and a detailed clinical examination, including peak expiratory flow rate measurements, to assess the prevalence of illness. Children in the industrial area were 2.3 times more likely to have unexplained episodic cough (95% confidence interval [CI] = 0.98, 10.3) and 2.8 times more likely to have rhinitis (95% CI = 1.1, 7.1). The adult population was 2.1 times more likely to have unexplained episodic cough (95% CI = 1.13, 7.09), 3.7 times more likely to have unexplained headaches (95% CI = 2.2, 6.3), and adults had a significantly greater reduction in expiratory flow (peak expiratory flow rate = 446 - 92x [industrial area] + 91x [male] - 0.8x [years lived in the area]).