In modern times, entrepreneurship is one of the main drivers of the economy of developed countries. Given the central role of the entrepreneur as an individual, it is no surprise that psychology is highly interested in this phenomenon. Like with every complex construct, it is difficult to unambiguously answer the question of the existence of the personality characteristics of an entrepreneur necessary for success in entrepreneurship and there have been many different findings on this topic. The aim of this research was to contribute to the research of psychological determinants of success in entrepreneurship by examining one of the key ones - need for achievement. Its implicit and explicit components were measured, the implicit one being assessed by using a promising but relatively unexplored method, the conditional reasoning test. A correlation research was conducted on 53 Croatian entrepreneurs and their 154 employees. Data was collected online and pen-paper method. Implicit and explicit need for achievement, entrepreneurial success with multiple measures, and personal characteristics of the entrepreneurs were examined. The results show that the implicit and explicit need for achievement are related to measures of success in entrepreneurship: a higher score on the measure of explicit need for achievement is associated with higher assessments of job growth, while a higher result on the measure of implicit need for achievement is associated with a higher assessment of job growth and entrepreneurial efficiency. In addition, it was found that the implicit need for achievement explains entrepreneurial success measured as entrepreneurial efficiency additionally to other measured variables. These results suggest the importance of considering the explicit and implicit need for achievement in guiding individuals into entrepreneurship, as well as in designing training to increase entrepreneurial performance.