Since its inception in 1966, the United Nations Joint Inspection Unit (JIU) has prevailed in the face of significant existential challenges. Against this backdrop, we investigate how and why the JIU persisted over time. Combining delegation and historical institutionalist approaches, we posit that entrepreneurial agents and layering processes together help us better understand persistence of international organizations. Based on semi-structured interviews with UN staff and JIU inspectors, we examine three critical junctures in the history of the JIU. Our results show that entrepreneurial agents and stakeholders in the JIU managed to avoid the closure or demotion of the JIU by engaging in a strategy of institutional layering. Our analysis, however, also demonstrates that the JIU survived at the price of losing its privilege as the central UN oversight body. These findings have implications for the study of international organizations and for the reform of the UN system at large.