Methotrexate (MTX)-induced hepatotoxicity is a significant clinical problem that may affect overall prognosis and disease outcome. Oxidative stress is a key player in its pathogenesis. The aim of this study was to investigate the role of ω-3 fatty acids as an adjuvant therapy in children and adolescents with acute lymphoblastic leukemia (ALL) during the maintenance phase of chemotherapy and the effect of ω-3 on MTX-induced hepatotoxicity.