For many years the molecular biology has been one of the most promising fields of science and its several methods have been used in practice. These new methods of molecular biology made impression on epidemiology and developed a new discipline, called molecular epidemiology. The molecular and predictive epidemiology play more and more important roles in the prevention of cancers. Early biomarkers could identify the high risk population to have the possibilities of primary preventive interventions. It uses both molecular biological methods and the elements of epidemiology. Its specificity is not high enough to establish the diagnosis but it can be used to follow the "minimal residual disease" and with markers of individual susceptibility, to assess the risk of tumors. As to the practice there are many problems because of the limited therapeutic possibilities, but the molecular and predictive epidemiology becomes an important part of medicine in the future.