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Immunotherapy in cancer is coming of age. Immune checkpoint inhibitors (ICIs), namely anti-CTLA4 and anti-PD1 antibodies, can lead to immune-related adverse events that may affect the gastro-intestinal tract. Enterocolitis is frequent and potentially serious. It is characterized by diarrhea accompanied by abdominal pain, and, more rarely, hematochezia. Toxic megacolon or colonic perforation may occur, particularly when treatment is delayed. Diagnosis is confirmed by colonoscopy or flexible sigmoidoscopy and biopsies. Infectious colitis, intestinal toxicity of other cancer treatments, and intestinal metastasis are the main differential diagnoses. The clinical characteristics of ICI enterocolitis resemble inflammatory bowel disease (IBD) flare-up, and, less frequently, microscopic colitis. In mild forms of ICI enterocolitis, symptomatic management will be sufficient and ICI therapy can be continued. Moderate to severe forms of ICI enterocolitis require ICI withdrawal, oral or intravenous corticotherapy, and, in about half of all cases, biotherapies. Resuming ICI therapy after complete remission of symptoms should be discussed on a case-by-case basis among oncologists and gastroenterologists. The risk of flare-up or ICI enterocolitis is about 40% in IBD patients receiving ICI. Recent data suggests that biotherapies could reduce overall survival in melanoma patients who are treated using ICIs.