Syndication increases the overlap of bank loan portfolios and makes them more vulnerable to contagious effects. We develop a novel measure of bank interconnectedness using syndicated corporate loan portfolios, overlap based on industry and region, and different weights such as equal weights, size and relationships. We find that interconnectedness is driven mainly by bank diversification, less by bank size or overall loan market size. Interconnectedness is positively correlated with different bank-level systemic risk measures including SRISK, DIP and CoVaR, and such a positive correlation mainly arises from an elevated effect of interconnectedness on systemic risk during recessions. Overall, our results highlight that institution-level risk reduction through diversification ignores the negative externalities of an interconnected financial system.