Our literature review on MTHFR gene polymorphism in male infertility patients indicates a significant association between C677T gene polymorphism and male infertility. Folic acid supplementation can improve sperm quality. The correlation between MTHFR gene polymorphisms and ED is questionable and needs to be confirmed by more clinical data. MTHFR gene polymorphisms are associated with homocysteine (Hcy) levels, which affects vascular endothelial function and may be related to the development of vascular ED (VED). Folic acid supplementation improves International Index for Erectile Function (IIEF) questionnaire scores in ED patients in whom phosphodiesterase 5 inhibitor (PDE5i) alone is ineffective.