Open innovation is still after a decade an emergent topic in literature and, because of this, there are few gaps to be explored. Two of these gaps are the relationship between open innovation and entrepreneurship and open innovation in small and medium enterprises (SMEs), because most studies focus on large enterprises. Our research question in this study is: what do case studies report in terms of open innovation in start-ups or SMEs that would be related to entrepreneurial orientation? Our study is a meta-synthesis of qualitative case studies following the stages presented by Hoon (2013). A theory was developed and presented considering the entrepreneurial orientation dimensions and open innovation activities. In the concluding section, limitations and suggestions in terms of future works were presented.