This article addresses the puzzle of why, and under what conditions, international organisations cease to exist. International Relations literature offers rich explanations for the creation, design and effectiveness of international institutions and their organisational embodiments, international organizations (IOs), but surprisingly little effort has gone into studying the dynamics of IO termination. Yet if we want to understand the conditions under which international organisations endure, we must also explain why they frequently fail to do so. The article formulates and tests a theory of ‘IO death’ using a combination of population-wide statistical analysis and detailed historical case studies. My analysis is based on an original dataset covering the period 1815–2016. I find that exogenous shocks are a leading proximate cause of IO terminations since 1815 and that organisations that are newly created, have small memberships, and/or lack centralised structures are most likely to succumb. My analysis leads me to suggest a number of extensions and refinements to existing institutionalist theories.