OBJECTIVES: To estimate health care costs for asthma patients with and without a COPD diagnosis. METHODS: Asthma patients with and without diagnosed COPD were selected from the HealthCore Integrated Research Database covering administrative claims from approximately 27.6 million people in the USA. The index event was a patient’s first exacerbation defined as oral corticosteroid prescription fills or emergency department visits or inpatient visits with a primary diagnosis of asthma. Eligibility criteria were ≥1 asthma diagnosis, ≥1 exacerbation and 12 months of continuous health plan enrolment on each side of the index date. Total all-cause and asthma-related direct health care costs for 12 months before and after the index date were calculated for all patients and those with and without a COPD diagnosis. RESULTS: 94,883 patients met all eligibility criteria, of these 15,127 (15.9%) had both asthma and COPD diagnoses. The mean patient age was 41.6 years and 62.4% were female. Co-morbid conditions were more common among asthma patients with a COPD diagnosis. Asthma-related direct costs represented 25-30% of all-cause direct health care costs for all patients. Among asthma patients, COPD and its associated co-morbidities roughly doubled all-cause and asthma related direct health care costs: mean annual pre-index all-cause health care costs were $20,012 (COPD diagnosis) versus $8,938 (no COPD diagnosis); mean annual pre-index asthma related costs were $5,623 (COPD diagnosis) versus $2,600 (no COPD diagnosis). Mean annual post-index costs were almost unchanged: all-cause costs of $21,692 (COPD diagnosis) versus $10,787 (no COPD diagnosis) and asthma-related costs of $5,242 (COPD diagnosis) versus $3,016 (no COPD diagnosis). CONCLUSIONS: The economic burden of asthma among patients with a COPD diagnosis in a US claims database is twice as high as those without a COPD diagnosis. Further research could adjust for the effects of age on the prevalence of co-morbidities among the different groups.