Chromosomal aneuploidy consists the leading cause of fetal death in our species. Around 50% of spontaneous abortions until 15 weeks of gestational age are chromosomally aneuploid, with trisomies accounting for 50% of the abnormal abortions. Trisomy 21 is the most common chromosome abnormality in liveborns and is usually the result of nondisjunction of chromosome 21 in meiosis in either oogenesis or spermatogenesis. To investigate the relationship between folate metabolism and Down syndrome (DS) in a Danish population, we analyzed the common 677C>T genetic polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene. Our cohort consisted of 181 mothers of children with DS versus 1,084 healthy controls. Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) were used to examine the MTHFR 677C>T polymorphism. No significant association between the polymorphism and the risk for DS was found. We conclude that the common MTHFR 677C>T polymorphism is not likely to be a maternal risk factor for DS in our cohort and that the difference to previous studies can probably be explained by small sample size or geographic variation in gene polymorphisms involving gene-nutritional or gene-gene or gene-nutritional-environmental factors.