This thesis examines the relationship between firm performance and the number of banking relationships for the publicly traded Turkish firms listed in the Borsa Istanbul (BIST) for the period 2003-2011, by using 2SLS model. In the analysis, banks are categorized according to their nationalities, ownership structures and orientations; firms are classified based on their size as small and large, the sample period is divided into two as crisis and non- crisis years, considering the effect of the 2008 global crisis on the Turkish economic and financial system. I find that firm performance decreases as the number of banking relationships increases, regardless of bank types. However, this negative relationship between firm performance and the number of banks is observed only in non-crisis times and for only small-sized firms. I also find that firm age, size, obtaining funding from external sources other than bank loans, belonging to a group, related lending, being a multinational company, incentives obtained from government and state-ownership are significant factors affecting the number of banking relationships. However, the significances of these variables differ for different bank and firm types, and for sub-periods.