The 2010s Haiti cholera outbreak was the first modern large-scale outbreak of cholera—a disease once considered under control largely due to the invention of modern sanitation. The disease was reintroduced to Haiti in October 2010, not long after the disastrous earthquake earlier that year, and since then cholera has spread across the country and become endemic, causing high levels of both morbidity and mortality. Nearly 800,000 Haitians have been infected by cholera, and more than 9,000 have died, according to the United Nations (UN). Following the outbreak's conclusion in February 2019, cholera transmission in Haiti is largely the subject of eradication efforts including WASH (water, sanitation, and hygiene), education, oral vaccination, and climate variability. Early efforts were made to cover up the source of the epidemic, but thanks largely to the investigations of journalist Jonathan M. Katz and epidemiologist Renaud Piarroux, it is widely believed to be the result of contamination by infected United Nations peacekeepers deployed from Nepal. In terms of total infections, the outbreak has since been surpassed by the war-fueled 2016–2021 Yemen cholera outbreak, although the Haiti outbreak is still one of the most deadly modern outbreaks. After a three-year hiatus, new cholera cases reappeared in October 2022.

Cholera is caused by the bacterium Vibrio cholerae that when ingested can cause diarrhea and vomiting within several hours to 2–3 days. Without proper treatment including oral rehydration, cholera can be fatal.

In January 2010, a 7.0 magnitude earthquake hit Haiti, killing over 200,000 people and further disrupting healthcare and sanitation infrastructure in the country. In the aftermath of the earthquake, international workers from many countries arrived in Haiti to assist in the response and recovery efforts, including a number of workers from countries where cholera is endemic. Before the outbreak, no cases of cholera had been identified in Haiti for more than a century, and the Caribbean region as a whole had not been affected by the cholera outbreak originating in Peru in 1991. The population's lack of prior exposure and acquired immunity contributed to the severity of the outbreak.

The suspected source of Vibrio cholerae in Haiti was the Artibonite River, from which most of the affected people had consumed the water. Each year, tens of thousands of Haitians bathe, wash their clothes and dishes, obtain drinking water, and recreate in this river, therefore resulting in high rates of exposure to Vibrio cholerae.

The cholera outbreak began nine months after the January 2010 earthquake, leading some observers to wrongly suspect it was a result of the natural disaster. However, Haitians grew immediately suspicious of a UN peacekeeper base, home to Nepalese peacekeepers, positioned on a tributary of the Artibonite River.

Neighboring farmers reported an undeniable stench of human feces coming from the base, to the extent that local Haitians began getting their drinking water upstream from the base.

In response, United Nations Stabilization Mission in Haiti (MINUSTAH) officials issued a press statement denying the possibility that the base could have caused the epidemic, citing stringent sanitation standards. The next day, 27 October 2010, Jonathan M. Katz, an Associated Press correspondent, visited the base and found gross inconsistencies between the statement and the base's actual conditions. Katz also happened upon UN military police taking samples of ground water to test for cholera, despite UN assertions that it was not concerned about a possible link between its peacekeepers and the disease. Neighbors told the reporter that waste from the base often spilled into the river. Later that day, a crew from Al Jazeera English, including reporter Sebastian Walker, filmed the soldiers trying to excavate a leaking pipe; the video was posted online the following day and, citing the AP report, drew increased awareness to the base. MINUSTAH spokesmen later contended that the samples taken from the base proved negative for cholera. However, an AP investigation showed that the tests were improperly done at a laboratory in the Dominican Republic, which had no prior experience of testing for cholera.

For three months, UN officials, the U.S. Centers for Disease Control and Prevention (CDC), and others argued against investigating the source of the outbreak. Gregory Hartl, a spokesman for the World Health Organization (WHO), said finding the cause of the outbreak was "not important". Hartl said, "Right now, there is no active investigation. I cannot say one way or another [if there will be]. It is not something we are thinking about at the moment. What we are thinking about is the public health response in Haiti." Jordan Tappero, the lead epidemiologist at the CDC, said the main task was to control the outbreak, not to look for the source of the bacteria and that "we may never know the actual origin of this cholera strain." A CDC spokesperson, Kathryn Harben, added that "at some point in the future, when many different analyses of the strain are complete, it may be possible to identify the origin of the strain causing the outbreak in Haiti."