Background: Little information is available regarding medical utilization and cost in patients with overlap syndrome of COPD and asthma. Purpose: To analyze medical utilization and cost in patients with overlap syndrome and to compare them to COPD patients without asthma. Methods: Using the 2009 Korean National Health Insurance (NHI) database, COPD patients were identified. Medical utilization and costs were also analyzed. Results: Of a total of 185,147 patients identified with COPD, 101,004 patients were classified with overlap syndrome of COPD and asthma and 84,143 patients with COPD without asthma. In 2009, the percentages of ER visits, admissions, and ICU admissions were 14.6%, 30.5%, and 0.5%, respectively, in the patients with overlap syndrome group and 5.0%, 14.1%, and 0.2%, respectively, in the COPD patients without asthma group (P＜0.05 for all comparisons). The cost of medical utilization was 790±71 US dollars per person and 3,373±4,628 dollars per person for outpatient and inpatient services, respectively, in the patients with overlap syndrome and 413±512 and 3,010±5,013, respectively, in the COPD patients without asthma (P＜0.05 for all comparisons). Multiple linear regression showed that age, sex, overlap syndrome, and hospitalization in the last year were significant factors affecting medical utilization and cost. Conclusions: In patients with overlap syndrome, both medical utilization and cost were higher than in COPD patients without.