The tragedy of the Haitian cholera epidemic-where a disease brought to the country by United Nations (UN) peacekeepers has killed at least 10,000 people and sickened over 800,000-has propelled a range of complex international law issues into the public eye. The repercussions of the ongoing debate over accountability, and the purposes and limits of UN immunity, are likely to reverberate for years to come. Despite considerable attention from the international law community, however, almost none of the resulting scholarship has focused on the international health law aspects of the case. The international spread of the vast majority of infectious diseases has been the subject matter of international law only since the 2005 revision of the International Health Regulations (IHRs). By contrast, preventing the international transmission of cholera has been the object of multilateral state negotiation for over 160 years, resulting in it becoming the sole subject matter of not merely the first, but the first three binding international health law treaties over a century ago. Since that time, cholera prevention has remained an unbroken thread woven through the history of international health law, from the initial International Sanitary Conventions, through the formation of the World Health Organisation, and into the twenty-first century. The current iteration of the IHRs are today one of the most universally accepted sources of binding international legal obligations of any kind; as the only disease that has appeared in all previous iterations over nearly 125 years, preventing the transnational spread of cholera approaches customary international law status. This chapter builds upon these themes to re-examine the conduct of the United Nations through this lens. It explores UN standards, and actual UN practice, as they relate to medical guidance to peacekeeping missions, preventative measures for peacekeepers such as vaccination and prophylaxis, and treatment of sewage and sanitation. In doing so, it offers valuable lessons from the past and the present on how international law around infectious disease might be effectively implemented, and followed, in the future.