Background: The presence of single nucleotide polymorphisms in the gene encoding key en-zyme in the folate pathway methyltetrahydrofolate reductase (MTHFR), causes methylation disorders associated with CAD development. Methods: Study group: 42 patients with CAD con-firmed by coronary angiography. Controls: 16 patients without CAD symptoms or significant coronary artery stenosis, based on invasive coronary angiography or multislice computed to-mography with coronary artery calcification scoring. Real-time PCR genotyping was assessed using TaqMan™ probes. Folic acid and 5-MTHF concentrations in blood serum were determined by LC-MS. Results: c.[1286A>C];[1286A>C] MTHFR polymorphism occurred significantly more often in (CAD+) patients compared to (CAD-) cohort and to the European population. The con-centration of 5-MTHF and folic acid in the subgroups of patients with methylation disorders di-vided by genotypes and (CAD+) was lower compared to (CAD-). Conclusions: The homozygous c.1286 A>C MTHFR variant can be considered as CAD genetic marker. In the subjects with the c.1286 A>C heterozygous and homozygous genotypes, lower concentrations of methyltetrahy-drofolate (5-MTHF) were observed. 5-MTHF can be considered as a biomarker of CAD. Identifi-cation of people at high risk of CAD using genetic tests can contribute to personalized therapy using active (methylated) form of folic acid (5-MTHF) in CAD patients with MTHFR polymor-phisms.