Folate mediated one-carbon metabolism is a complex biochemical pathway that is essential to the cell. Therefore, any impairments or deficiencies can have serious health consequences. Examination of the relationship between folate status and DNA methylation in pregnant women showed differential methylation patterns between individuals in the DHFR gene, however, the differences observed was not associated with folate status. The 19 bp deletion / insertion polymorphism (DIP) within the DHFR gene, an enzyme that catalyses the reduction of dihydrofolate to tetrahydrofolate has been studied extensively in association with both neural tube defects and folate metabolites but the results are controversial. Screening the DHFR 19 bp DIP in the largest cohort yet to address this issue and assessment of the DIP with folate metabolites and folate status showed no association between the DIP and the folate metabolites or folate status. DHFRL1 is a newly discovered reductase enzyme that participates in thymidylate biosynthesis in the mitochondria. Recombinant and endogenous DHFRL1 polymorphisms examined for functionality showed the polymorphisms to be capable of altering enzyme activity and to be associated with neural tube defects. By altering DHFRL1 expression numerous genes have been shown to be affected. The findings above have demonstrated the importance of the genes involved in folate metabolism and their relevance for human health and disease.