This paper studies how a bank's diversification affects its own risk taking behavior and the risk taking of competing, nondiversified banks. By combining theories of bank organization, market structure and risk taking, I show that greater geographic diversification of banks changes a bank's lending behavior and market interest rates, which also has ramifications for nondiversified competitors due to interactions in the banking market. Empirical results obtained from the U.S. commercial banking sector support this relationship as they indicate that a bank's risk taking is lower when its competitors have a more diversified branch network. By utilizing the state-specific timing of a removal of intrastate branching restrictions in two identification strategies, I further pin down a causal relationship between the diversification of competitors and a bank's risk taking behavior. These findings indicate that a bank's diversification also impacts the risk taking of competitors, even if these banks are not diversifying their activities.