Homocysteine (Hcy) is an endogenous, non-structural protein, a sulfur-containing amino acid emerging on the pathway of methionine and cysteine, actively involved in numerous biochemical reactions. Total concentration of homocysteine in plasma of healthy humans is low and its level is between 5.0 and 15.0 mmol/l, assessed with the use of HPLC, or 5.0-12.0 mmol/l, using immunoassay methods. Higher concentration of this amino acid in blood is called hyperhomocysteinemia. Hyperhomocysteinemia is significantly correlated with cardiovascular disease and its complications: heart attacks and strokes. It is believed that hyperhomocysteinemia damages endothelial cells, reduces the flexibility of vessels, and adversely affects the process of hemostasis. In addition, hyperhomocysteinemia enhances the adverse effects of risk factors such as hypertension, smoking, and impaired glucose, lipid and lipoprotein metabolism, as well as promoting the development of inflammation. The concentration of homocysteine can be effectively lowered by supplementation with folic acid and vitamins B12 and B6. However, intervention studies conducted in the past decade did not confirm the clinical benefit of vitamin therapy lowering the level of homocysteine in blood of patients with cardiovascular disease. Moreover, there is not clear evidence from genetic studies that the presence of the gene for MTFHR polymorphism 677C>T, which is one of the most common causes of hyperhomocysteinemia, is also associated with the development of cardiovascular disease. These results led the researchers to discuss the role of homocysteine in the development and treatment of cardiovascular disease as well as the need for further research on this issue.