This study was a nationwide, population-level, historical cohort study of patients with acute leukemia who underwent allo-HCT. This data was obtained from the claims database of the NHIS of the Republic of Korea. South Korea has a universal health coverage system provided by the central government, which has been unified since 2000. The NHIS provides health insurance to more than 99% of the population. Accordingly, the NHIS has a comprehensive health database for diagnoses, treatments, procedures, and prescriptions. They provide these extensive data for use in research after the approval process. This study also obtained death related data, including the cause of death from Statistics Korea, which has a comprehensive database in connection with the NHIS. In South Korea, death registration is usually completed and confirmed by a physician. The institutional review boards of Kosin University Gospel Hospital approved this study and granted a waiver of informed consent from the study participants owing to the nature of the data from which private information was deleted. All methods were carried out in accordance with relevant guidelines and regulations along with the approval.