Methylenetetrahydrofolate reductase (MTHFR) is involved in DNA methylation and nucleotide synthesis. Accumulated evidence has demonstrated that C677T and A1298C polymorphisms of the MTHFR gene are associated with acute lymphoblastic leukemia (ALL) risk, but the results have been inconclusive. To determine a more precise estimation, we performed a meta-analysis of 28 studies with 4240 cases and 9289 controls. We found that the 677TT genotype showed a reduced risk of ALL compared with the 677CC genotype in the overall population (odds ratio [OR] 0.76, 95% confidence interval [CI] 0.61-0.92). The reduced risk was pronounced only among the Caucasian population (OR 0.68, 95% CI 0.51-0.90), not the Asian (OR 0.89, 95% CI 0.75-1.05). For the MTHFR A1298C polymorphism, no significant association with ALL susceptibility was observed in the pooled analyses. However, significantly increased ALL risk was found in childhood in the comparison of 1298CA versus AA genotype. This study provides evidence that MTHFR polymorphisms may play an important role in the development of ALL.