Abstract Banks lend through syndicates to diversify risk, but co-lending relationships are sticky. This paper finds a “co-lender effect”, namely that banks’ lending volumes are impacted by shocks to co-lenders. We create a new database of cross-border syndicated lending to developing countries from 1993 to 2020. We characterize the network and, as suggested by theory, find both resilience and fragility. Central players propagate shocks, while the impacts of fringe banks are negligible. The global financial crisis and the growth of South-South lenders prompted a decline in network centrality and higher network density with more connections between a declining number of participants. We find further support for a co-lender effect, compounding the sharp fall in lending during the Covid-19 crisis, employing a different methodology.