Methylenetetrahydrofolate reductase (MTHFR), a key enzyme in folate metabolism, plays a major role in the provision of methyl groups for DNA methylation and in the production of dTMP for DNA synthesis. Different polymorphisms have been described for this enzyme, the most studied being the C677T, which has been shown to be associated with predisposition to colorectal cancer in patients who consume a high alcohol diet. The aim of this study was to determine whether the MTHFR polymorphism is related to hepatocellular carcinoma (HCC) in patients with alcoholic cirrhosis. MTHFR genotypes were determined in 300 liver transplant patients, 72 of whom had alcoholic cirrhosis with HCC and 122 of whom had alcoholic cirrhosis without HCC. The remaining patients were transplanted for HCC on normal liver (n = 27) or viral cirrhosis with HCC (n = 49) or without HCC (n = 30). We also tested 80 healthy subjects. Among the group of patients transplanted for alcoholic cirrhosis, the frequency of MTHFR variants CC versus CT and TT was significantly higher in patients with HCC than in patients without macroscopic evidence of HCC (P = 0.02). This difference was not observed between patients with and without HCC developed either on viral cirrhosis or on non-cirrhotic liver. If we considered all the patients transplanted for HCC, the MTHFR CC genotype was significantly higher in patients who had developed HCC on alcoholic cirrhosis rather than on viral cirrhosis (P = 0.002) or on non-cirrhotic livers (P = 0.02). The relative risk for HCC in subjects with alcoholic cirrhosis and the CC genotype was 2.03. These results suggest that the MTHFR CC genotype increases the risk to develop HCC in patients who consume a high alcohol diet.