A large proportion of small and medium-sized enterprises are managed by their owners and founders. The goal of this research was to describe the diversity of management practices in owner-managed SMEs. Understanding this diversity will raise awareness of the challenges SMEs are facing and suggest possible solutions that will help improve their management and sustainability. In this study, 205 owner-managed SMEs with more than nine people employed were analyzed using a company self-assessment based on a tailor-made governance model. Data were analyzed using statistical analysis software in combination with a visual analysis. To group similar companies, the cluster analysis technique was used. The results showed a high diversity in how companies were managed and their performances. This research indicated that statistical analysis itself is not sufficient for exploring this diversity, and other approaches, such as visual analysis, must be used as well.