The purpose of this study was to investigate the role of genetic polymorphisms associated with venous and arterial thrombosis in patients with retinal vein occlusion (RVO). One-hundred and two consecutive patients with RVO were examined for factor V G1691A and factor II G20210A, methylenetetrahydrofolate reductase (MTHFR) C677T and apolipoprotein E4 by amplification of specific DNA fragments and restriction analysis. The risks exerted by these polymorphisms and by the conventional risk factors of RVO were evaluated by comparing their frequencies among patients and controls and by estimating the respective odds ratios. We found that the prevalences of the factor V G1691A, factor II G20210A, and apolipoprotein E4 polymorphisms were similar in the study and control groups. Logistic regression analysis involving the parameters for which significant differences were detected disclosed an odds ratio of 1.9 for MTHFR C677T homozygosity (95% confidence interval 0.95-3.81), an odds ratio of 2.12 for hypertension (95% confidence interval 1.16-3.73) and an odds ratio of 3.25 for a family history of stroke (95% confidence interval 1.07-9.51). Our data suggests that homozygosity for the MTHFR C677T polymorphism is a risk factor of RVO in addition to arterial hypertension and a family history of stroke.