Acute severe colitis is a potentially life-threatening medical and surgical emergency requiring hospitalization and intensive monitoring. The diagnosis of severe acute colitis is based on clinical and biological criteria. Colectomy should be discussed at each stage of management and is indicated immediately in case of complications. Thromboembolic prevention with low molecular weight heparin is essential in any patient with severe acute colitis. The first-line medical treatment is intravenous corticosteroid at a dose of 0.8mg/kg/day of prednisone equivalent. In case of failure, a second line of medical treatment can be attempted in the absence of complications. The two possible treatments are infliximab and ciclosporin.