The aim of this study was to evaluate whether the cytosine-to-thymine mutation at base 677 of the methylenetetrahydrofolate reductase gene (MTHFR C677T), which has been associated with neural tube defects and congenital oral cleft, is also associated with tetralogy of Fallot (TF), a congenital heart disease. The MTHFR C677T genotype was investigated in a sample of 38 children born with TF who underwent surgical repair in early life. Two hundred and fifty-one healthy individuals were included as controls for allele and genotype frequencies. We found a higher prevalence of the T allele in TF compared to the control group (OR = 1.675; 95% CI [1.022-2.743]; p = 0.05). The TT genotype increased by 4.856 the risk for this congenital disease (95% CI 1.308 12.448; p = 0.028). Our results suggest that MTHFR polymorphism can be considered a susceptibility gene for this congenital heart disease.