Using Ontario healthcare administrative databases, over 228,000 children aged 0 to 9 years were identified as having asthma between 1994 and 1998 and followed until they turned 10 years old or the end of the study. The prevalence of childhood asthma increased by 35% during the study period. These children had a higher healthcare utilization and cost over $100 more per child per year than the general population, and contributed to over one third of the total Ontario Health Insurance Plan expenditures. Findings of this study revealed an enormous burden of illness to children with asthma and the healthcare system.