Small and medium enterprises carry out their activities in a dynamic environment that is affected by various processes that also impact their sustainability. The future has the companies that are able to respond promptly to the challenges and are able to exploit opportunities sufficiently. One form of modern entrepreneurship that could help SMEs' sustainability in this environment is the cluster cooperation. This form of entrepreneurship brings many positive effects, but is also affected by various risks. The main aim of this study is to assess the perception of selected business risks that have an impact on SMEs' engagement into cluster cooperation. Using the questionnaire surveys of 1004 SMEs the perception was evaluated with emphasis on the differences between micro-small-and medium sized enterprises. From the data obtained, the tendencies are exposed through the evaluation of following risk categories such as: Market risks, Relation risks, Common resources risks, Operational risks, and Competency risks being assigned by a particular risk indicator afterwards. The final evaluation being made upon all respondents' answers analysis has confirmed that the competition risk turned out to be the most important risk indicator.