Lately the role of homocysteine in pathology of diseases, also neurological seems to be very interesting. Homocysteine is an amino acid containing thiol group, produced in body by demethylation of methionine. An important role in its metabolism play vitamins from group B (vitamin B6 and B12), folic acid and enzymes: reductase and synthase. The level of homocysteine depends on genetic and congenital factors. Normal concentration of homocysteine in serum for people under 60 years old is 5-15 mmol/l, for older it is higher. Recently there was found the correlation between the excess of homocysteine and the risk of vascular diseases, dementia. It is also interesting if the level of homocysteine changes in patients with Parkinson’s disease. It can also be teratogenic. It was found that in epileptic patients the level of homocysteine is higher. Antiepileptic drugs which induce cytochrome P450 cause increase in homocysteine levels.