In the present retrospective study we aimed to investigate the association of selected polymorphisms in genes involved in the folate and methionine pathway (MTHFR 677C>A, MTHFR 1298A>C, MTRR 66A>G, MTHFD1 1958G>A, BHMT 742G>A, GNMT 1298C>T), as well as polymorphisms of PACSIN2 (rs2413739) and ITPA (94C>A and IVS2+21A>C), and long-term outcome and relapse rates in pediatric ALL patients undergoing maintenance therapy with 6-MP. The gene discussed is MTHFR; the disease is acute lymphoblastic leukemia.