Is the methylation status of the methylenetetrahydrofolate reductase (MTHFR) promoter region in semen samples associated with orecurrent spontaneous abortion' (RSA)? MTHFR promoter hypermethylation is more frequent in semen samples from RSA couples than in semen samples from infertile couples with no history of RSA (NRSA) and affects the whole sperm population significantly more often. Modifications to the MTHFR gene such as polymorphisms and promoter methylations are associated with male infertility. Retrospective cohort study of semen samples from 20 RSA couples, 147 NRSA couples and 20 fertile men between 2011 and 2012. DNA from the semen samples of RSA, NRSA and fertile men were analyzed by methylation-specific PCR amplification using primers which anneal to the methylated or unmethylated cytosine-phosphodiester bond guanine (CpG) islands within the promoter region of MTHFR. The specificity of the PCR products was assessed by DNA sequencing. The methylated MTHFR epigenotype (including samples where it co-existed with unmethylated MTHFR epigenotypes) was detected in 75 of RSA men, 54 of NRSA men and 15 of fertile men. MTHFR methylation was observed in the whole sperm population in semen samples from 55 of RSA men compared with 8 in NRSA men (P 0.05) and 0 in fertile men (P 0.05). DNA sequencing analysis was fully concordant with the PCR results and revealed that when MTHFR methylation occurred, CpG islands within the promoter region were 100 methylated (hypermethylation of MTHFR promoter). The relatively small sample size of RSA infertile couples. The hypermethylation of the MTHFR gene promoter should be taken into consideration as a novel putative risk factor in RSA etiology. Our institution has received an FAR research grant from the University of Ferrara, Ferrara, Italy. No competing interests declared.