The importance of relationship marketing and its beneficial impact to organizations are now widely recognized. However, its actual adoption within the banking sector is still disputed. In fact, banks have been historically viewed as organizations less exposed to competition and as such less oriented to engage in marketing practices. Moreover, the traditional retail banking approach to customers has been in the past too focused on products. This implied a widespread adoption of transaction marketing models that only in recent years have been, at least partially, replaced by relationship marketing practices. In this perspective, the effectiveness of relationship marketing in the banking sector is still under scrutiny, and the purpose of this research is to identify and measure it within the context of a medium sized bank and with specific regard to the Small and Medium Enterprises (SME) segment. Furthermore, the scope of the research has been extended to identify possible patterns revealing under which conditions and over which clusters of clients, relationship marketing has the highest probability to deliver benefits to the adopting organization in a B2B setting.