Oncological treatment has been revolutionised by the advent of immune checkpoint inhibitors (ICPi), which block inhibitory immune pathways to enhance anti-tumour responses and improve survival. This mode of action is non-specific so can cause immune-related adverse events, of which diarrhoea and enterocolitis are amongst the most common. ICPi-enterocolitis frequently leads to cancer therapy interruption. ICPi-gastritis typically occurs at a later stage of ICPi therapy and can present more insidiously with nausea and vomiting. ICPi-enterocolitis and gastritis are treated with corticosteroids, with refractory cases typically requiring biologic therapy. This review will briefly consider the pathogenesis of ICPi-induced GI disease, before focussing on the practical management of these conditions. The anticipated global increase in ICPi use across cancer types highlights the importance of prospective research in order that we can understand the immuno-microbiology of ICPi-enterocolitis and gastritis. This will lead to predictive biomarkers and help to define optimal treatment regimens.