The structure of economy is very heterogeneous. It consists of enterprises doing business in various branches and, accordingly, belonging to various sectors and various industries within them. In order to do their businesses with as much quality as possible, enterprises opt for various legal forms and thus operate as partnerships, limited partnerships, limited liability companies, joint stock companies and state-owned enterprises. Finally, enterprises belonging to a national economy can be dramatically different in terms of their size, measured by the number of their employees, level of total assets, level of generated revenues or their contribution to the creation of value added. This paper puts stress on the overview of enterprise performance from their size's point of view. In the first few parts of the paper, special attention is paid to the research regarding the importance of enterprise size to economic performance and, accordingly, positioning big, medium sized and small enterprises in Serbian economy. Central part of the paper pays attention to the overview of return potential of Serbian economy in terms of enterprise size. Finally, at the end of the paper we emphasize the problems of volatility regarding the performances of big, medium sized, and small enterprises, as well as the influence of operating and financial leverage on their performance.