Introduction. Homocysteine is an amino acid that is formed in the metabolism of methionine as the quantitatively most important metabolite. Its chemical structure has been known for 90 years and its biological roles are still being investigated. Under normal conditions, homocysteine is present in plasma at the concentration of 5 - 9 mmol/l. When the cell capacity for homocysteine is reached, it is transported to the extracellular space, until the intracellular level is normalized. If the cell is unable to reach the required levels of homocysteine, it accumulates in the blood and hyperhomocysteinemia occurs. Discussion. It has been determined that many factors, such as congenital enzyme deficiency, age, sex, inadequate diet (vitamin B complex deficiency) increase the level of homocysteine in the blood. Impaired kidney function, diabetes, hyperthyroidism, as well as many medications, can have an effect on homecysteinemia. Increased concentration of homocysteine in the blood accelerates the process of atherosclerosis by several different mechanisms and represents an independent risk factor for the occurrence of cardiovascular diseases and adverse cerebral events. The prevalence of hyperhomocysteinemia is estimated at 5% in the general population and 13 - 47% among patients with symptomatic atherosclerotic vascular disease. Conclusion. For these reasons, the level of homocysteine in the blood should be monitored and corrective measures should be implemented, which include sufficient intake of folic acid, vitamins B12 and B6, in doses that depend on fasting homocysteine levels and after the methionine load test.