Children with asthma use significantly more health services than other children, yet the majority of their health care costs are for nonasthma services. The objective of this study was to measure the impact of asthma and specific upper respiratory comorbidities on the use and cost of health care by children. A population-based historical cohort study from January 1, 1992 to December 31, 1992 was conducted. Multiple visits for otitis media, sinusitis, and allergic rhinitis were considered comorbidities. The outcome measures were nonurgent outpatient care, pharmacy fills, urgent care visits, and hospital care along with the associated total costs. Children between ages 1 and 17 years were studied (n = 71,818). Children with asthma were more likely than children without asthma to have a comorbidity (26% vs. 9%). Children with multiple visits for otitis media, sinusitis, and allergic rhinitis were 1.8, 4, and 12 times more likely, respectively, to have a diagnosis of asthma in the same year. Children with asthma had a 47% probability of being in the highest total cost quintile compared to a 29% likelihood once adjusted for comorbidities. Visits for otitis media, sinusitis, and particularly allergic rhinitis appear to be overrepresented in children with asthma and contribute to their high utilization rate. Once a high-risk cohort is identified, the needs of those children can be addressed through targeted, organized systems of care that may include guidelines or other disease management strategies.