The Kosi flood disaster of 2008 in Bihar and also in Nepal highlights two key issues relating to flood control. The first is the failure of the structural approach to flood control on the Kosi and the second is institutional dysfunction with respect to trans-boundary flood management. This article discusses the key reasons for the failure of flood management in the Kosi, through stakeholder interviews and observations in the aftermath of the flood. The institutional context comprises several challenges such as trans-boundary politics between Nepal and India, the internal politics of Nepal, intra-state politics in India, the inherent weaknesses of the Kosi treaty, structural flood control strategy and the lack of connection between governmental decision-making bodies, implementation agencies and civil society.