BACKGROUND: Few studies have examined survival in relapsed childhood acute lymphoblastic leukemia (ALL) in resource-limited countries. The aims of this study were to evaluate the incidence, prognostic factors, and survival of relapsed childhood ALL in Thailand. METHODS: The medical records of patients with ALL aged <15 years in the major tertiary care institution in Southern Thailand between January 2000 and December 2019 were retrospectively reviewed. The Kaplan-Meier method was used to depict the overall survival (OS). RESULTS: A total of 472 patients with ALL were enrolled. The incidence of relapsed ALL was 32.8%. Of the 155 relapsed patients, 131 (84.5%) and 24 (15.5%) had B-cell and T-cell phenotypes, respectively. One hundred thirteen (72.9%) and 42 (27.1%) patients had early and late relapses, respectively. The most common site of relapse was bone marrow in 102 patients (65.8%). One hundred twenty-eight (82.6%) and 27 (17.4%) patients received or refused the relapse chemotherapy, respectively. The 5-year OS of all relapsed patients was 11.9%. The 5-year OS among the patients with early relapse was significantly lower than in the patients with late relapse (5.3% vs. 29.1%, respectively, p <0.0001). Site and immunophenotype were not associated with survival of relapsed ALL. The patients who refused chemotherapy had a median survival time of 3.1 months. CONCLUSION: The relapse rate was one third of patients with ALL. The 5-year OS was 12% and patients who refused chemotherapy had a median survival time of 3 months.