Epigenetics is the scientific discipline within the field of biology which studies heritable changes that are not caused by a change in a DNA molecule. Special attention is focused on the importance of epigenetic mechanisms in the regulation of chromatin organization and gene expression, and their changes by environmental and external factors can trigger tumor development by activation of oncogenes or inactivation of tumorsuppressors. The most explored epigenetic modification is DNA methylation. It represents a covalent addition of methyl groups to cytosine ring in cytosine-guanine dinucleotide complex. Gene promoter methylation leads to heterochromatization. Choriocarcinoma is a malignant tumor of epithelial chorionic villi which is often accompanied with acquired genomic abnormalities. It is characterized by early hematogenous spread and clinically manifests with poor vaginal bleeding. Histopathologic diagnosis is the gold standard and the therapy is based on the combination of one or more chemotherapeutic agents Choriocarcinoma cells show an increased total level of methylation in the gene promoter regions as compared with the physiological trophoblast cells. Tumorsuppressor genes are hypermethylated, including regulators of the cell cycle, the genes responsible for the repair and protection of DNA, apoptosis, cell adherence and the process of metastasis. Drugs that inhibit DNA methylation known as demethylating agents, most notably decitabine, are under extenisive research.