Entrepreneurship is the driving force of the economy; however, only successful business activity offers a wide range of benefits. Researchers and entrepreneurs have a diversified understanding of entrepreneurial success given that its measurement, while frequently desirable in practice, is difficult. Unfortunately, neither the literature nor the practice offers an appropriate instrument to diagnose entrepreneurial success in all of its complexity. This article constitutes an initial report on the development of a research tool, the Questionnaire of Entrepreneurial Success (QES), to diagnose entrepreneurial success. This study uses six research tools to examine 144 entrepreneurs operating in Poland whose companies were set up between 1983 and 2013. A preliminary analysis of the psychometric parameters demonstrates that the experimental version of the QES exhibits high reliability, whereas analyses aimed at determining theoretical accuracy reveal the expected correlations with other indicators of entrepreneurial success.