The article examines the relationship between the size of the shadow economy and indicators of the investment market development. Net inflow of foreign direct investments, volume of net investments in non-financial assets, volumes of portfolio investments, and net outflow of foreign direct investment were used as parameters characterizing the development of the investment market. The dependence between the indicators was analyzed using the regression equation, Shapiro-Wilk test. Research results demonstrate that the increase in the inflow and outflow of foreign direct investments leads to an increase in the size of the shadow economy without a time lag in Ukraine, Poland, Slovenia, Romania, Croatia, Lithuania, Latvia, Estonia, and with a time lag of 1 year in Slovakia and Hungary. The largest impact on the size of the shadow economy is made by the volume of inflow and outflow of direct foreign investments, while the volume of portfolio investments has a less significant effect. Consequently, it was concluded that the processes of inflow and outflow of direct foreign investments require enhanced control by specialized state executive bodies given the scale of their potential destabilizing impact on the macroeconomic stability of the country.