Changes in the prevalence of asthma among Canadian children.

The prevalence of childhood asthma is rising, particularly among boys, among 0- to 5-year-olds and 10- to 11-year-olds, and among children in households where adults smoke. Whether the increase is due to an improvement in physicians' ability to recognize and diagnose asthma, or whether the underlying causes are becoming more widespread, cannot be determined from this analysis and warrant further study.