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Folate deficiency due to the methylenetetrahydrofolate reductase (MTHFR) and methionine synthase (MS) variants leads to carcinogenesis by affecting DNA synthesis, repair, and methylation. We hypothesized that the MTHFR C677T, A1298C, and MS A2756G polymorphisms are associated with risk of bladder cancer. In a case–control study of 239 bladder cancer cases and 250 cancer-free controls, we found that the MTHFR 677TT genotype was statistically significantly associated with an increased risk of bladder cancer compared with the 677CC genotype (OR = 2.06, 95% CI = 1.16–3.64). Furthermore, the TA haplotype was associated with a significantly increased bladder cancer risk (OR = 1.38, 95% CI = 1.05–1.81) than was the most common haplotype, CA (e.g., CA denotes MTHFR 677C -1298A). We also found that the combined genotypes with 4–6 variant (risk) alleles (i.e., MTHFR 677T, 1298A, and MS 2756G alleles) were associated with an increased risk of bladder cancer (OR = 1.62, 95% CI = 1.03–2.53) compared with those with 0–3 variants, and this increased risk was more pronounced among subgroup of older people (OR = 1.71, 95% CI = 1.03–2.83). A meta-analysis of seven studies did not show a significant risk of bladder cancer in the MTHFR polymorphisms. The MTHFR polymorphisms and their haplotypes appear to jointly contribute to risk of bladder cancer. [ABSTRACT FROM AUTHOR]