Epigenetics has become a major field of reproductive medicine after the epigenetic regulation of gene expression was discovered. The aim of this study was to find out whether or not methylenetetrahydrofolate reductase (MTHFR) gene promoter hypermethylation in the spermatozoa of men who were offered assisted reproduction is associated with idiopathic male infertility. Sperm DNAs from 40 idiopathic infertile men with normozoospermia and 40 controls consisting of healthy fertile men were isolated. Following the modification of DNAs by sodium bisulphite, the methylation status of the MTHFR gene promoter was quantified by pyrosequencing. No significant differences were observed between the clinical characteristics of patients and controls. The percentage of MTHFR promoter methylation in infertile men with normozoospermia (11%) was significantly higher than that in the healthy control (4.3%) group (p=.01). A 9.5% of methylation level was determined via receiver operator characteristic (ROC) analysis as the cut-off value. There were 21 (53%) hypermethylated men among the infertile men and 2 (5%) in the control group (p=.0001). The intragroup analysis of the infertile group did not reveal any statistically significant differences in terms of overall clinical characteristics between hyper-and normo-methylated infertile men. Our results suggest that epigenetic silencing (hypermethylation) of MTHFR could result in an elevated risk of male infertility.