This study measured the impact of the Decisions on Life-Sustaining Treatment Act by analyzing medical cost data from the National Health Insurance Service-National Sample Cohort. After identifying the patients who died in 2018 and 2019, the case and control groups were set using the presence of codes for managing the implementation of life-sustaining treatment with propensity score matching. Regarding medical costs, the case group had higher medical costs for all periods before death. The subdivided items of medical costs with significant differences were as follows: consultation, admission, injection, laboratory tests, imaging and radiation therapy, nursing hospital bundled payment, and special equipment.This study is the first analysis carried out to measure the impact of the Decision on LifeSustaining Treatment Act through a cost analysis and to refute the common expectation that patients who decided to withhold or withdraw life-sustaining treatment would go through fewer unnecessary tests or treatments.