Objectives: Ambient ozone (O3) exposure is associated with a variety of health conditions. The objective of this study was to examine the effect of increased daily concentrations of ozone on emergency department (ED) visits due to lower respiratory diseases (LRD), such as acute or chronic bronchitis, in Edmonton, Canada. Materials and Methods: Data concerning 10 years (1992-2002) were obtained from 5 Edmonton hospital Emergency Departments. Odds ratios (ORs) for ED visits associated with the increased ozone levels were calculated employing a case-crossover technique with a time-stratified strategy to define controls. In the constructed conditional logistic regression models, adjustments were made for daily number of influenza ED visits and weather variables using natural splines. ORs and their 95% confidence intervals (95% CI) were reported in relation to an increase in the interquartile range (IQR = 17.9 ppb) of the ground-level ozone. Results: Overall, 48 252 ED visits due to LRD were identified, of which 53% were made by males. The presentations peaked in December (12%) and February (11.7%) and were the lowest in August (5.6%). Positive and statistically significant results were obtained for acute bronchitis: for same day (OR = 1.09, 95% CI: 1.05-1.13, lag 0) and for lag 2, lag 3-7 and 9 days; for chronic bronchitis: for lag 6, 7, and lag 9 days (OR = 1.11, 95% CI: 1.05-1.18, lag 9). For all ED visits for LRD, lag 0, lag 1, and lag 3-9 days showed positive and statistically significant associations (OR = 1.06, 95% CI: 1.03-1.09, lag 0). Conclusions: These findings support the hypothesis concerning positive associations between ozone and the ED visits due to LRD.