To date there has been little investigation of the prevalence of comorbid conditions in asthma patients. Using 1996/97 cross-sectional health services administrative data for British Columbia, we compared the prevalence of comorbid conditions in treated adult asthma patients with the general adult population using a standardized comorbidity identification methodology, the Adjusted Clinical Group (ACG) Case-Mix System. We also profiled the comorbidity burden of pediatric asthma patients. Adults with asthma were significantly more likely to have a range of comorbidities, including respiratory infections, allergic rhinitis and 8 high impact/high prevalence chronic conditions (HIHPCCs). One in 4 adults with asthma had depression, the most prevalent HIHPCC. Children with asthma had a lower comorbidity burden than adults, but 12.6% had a stable or unstable chronic medical condition, with the most prevalent HIHPCC also depression. Adults with asthma had a high and complex comorbidity burden, particularly in terms of multiple chronic conditions. We discuss the implications for services planning and delivery.