Purpose: This study was to identify health-related quality of life of Korean young adults and elderly with multimorbidity and to examine factors influencing their health-related quality of life. Methods: Health-related quality of life was measured by the Korean version of the EQ-5D. Using a descriptive study, the study incorporated a secondary analysis of the Korean version of the EQ-5D data from the 8th wave of the Korea Health Panel Survey in 2013. Selected demographic data and the Korean version of the EQ-5D were analyzed using x2-test, t-test, ANOVA and multiple regression analysis. Results: Education, drinking, type of health insurance, and number of chronic disease significantly affected the health-related quality of life in the young adults with multimorbidity. Educational level, occupational type, drinking, physical activity, number of chronic disease, unmet healthcare need and the type of multimorbidity significantly affected the health-related quality of life in the elderly with multimorbidity. Conclusion: The factors influencing health-related quality of life were different for young adults versus elderly with multimorbidity. Therefore, there is a need for age-specific health care programs that may improve health-related quality of life of adults with multimorbidity.