Guerrilla marketing is a relatively new way of doing marketing. It is initially used by small companies and/or individuals allowing them to act like large companies. However, more and more large companies use Guerrilla marketing these days. The usage of Guerrilla management can bring advantages but can also increase risks. At this moment little research is done about the way how large companies manage the reputational risk associated with Guerrilla marketing. This is a problem in both science and practise. The purpose of this thesis is therefore to contribute to the understanding of how large companies manage the possible reputational risk that Guerrilla marketing and the communication of Guerrilla marketing brings along. This research is based on several theories, both emerging and dominant about Guerrilla marketing, Viral Marketing, Buzz marketing, Reputational risk and Reputational Risk Management. To do the research, in-depth interviews were held with experts when it comes to managing reputational risk and new marketing tools of four large companies based in Sweden. The analyses show that large companies manage the increasing reputational risks in some extend. Main findings are that the companies do not monitor Guerrilla marketing processes and do not have a central coordination for reputational risk management. This shows that not all companies are really aware of the risk that new marketing tools bring along and do not have a solid reputational risk management.