BackgroundThe prevalence of multiple chronic conditions (MCC), defined as several coexisting chronic conditions, has increased with the aging of society. MCC is associated with poor outcomes, but most comorbid diseases in asthma patients have been evaluated as asthma-associated diseases. We investigated the morbidity of coexisting chronic diseases in asthma patients and their medical burdens.MethodsWe analyzed data from the National Health Insurance Service-National Sample Cohort for 2002–2013. We defined MCC with asthma as a group of one or more chronic diseases in addition to asthma. We analyzed 20 chronic conditions, including asthma. Age was categorized into groups 1–5 (< 10, 10–29, 30–44, 45–64, and ≥ 65 years, respectively). The frequency of medical system use and associated costs were analyzed to determine the asthma-related medical burden in patients with MCC.ResultsThe prevalence of asthma was 13.01%, and the prevalence of MCC in asthmatic patients was 36.55%. The prevalence of MCC with asthma was higher in females than males and increased with age. The significant comorbidities were hypertension, dyslipidemia, arthritis, and diabetes. Dyslipidemia, arthritis, depression, and osteoporosis were more common in females than males. Hypertension, diabetes, COPD, coronary artery disease, cancer, and hepatitis were more prevalent in males than females. According to age, the most prevalent chronic condition in groups 1 and 2 was depression, dyslipidemia in group 3, and hypertension in groups 4 and 5. Older age, low income, and severe disability were independent risk factors for MCC in patients with asthma. The frequency of asthma-related medical system use and asthma-associated costs increased with increasing numbers of coexisting chronic diseases.ConclusionComorbid chronic diseases in asthma patients differed according to age and sex. The asthma-related-medical burdens were highest in patients with five or more chronic conditions and groups 1 and 5.