The article is devoted to the underground economy research. The underground economy size evaluation methods are scrutinized. Rough estimations of the size of the underground economy, based on different approaches, are mentioned. The authors put forward a hypothesis of balance between the official and underground economies according to which it becomes apparent only through correlation of their main purposes. Therefore, the underground economy size can be evaluated by comparison of the evolution of per capita income in a certain region or in a individual country as well as the quality of life indicators evolution and natural environment assessment in a certain region or in a individual country during the same period of time.