[en] The authors report the case of a patient aged 60-year-old who survived ulcerative colitis complicated by toxic megacolon and disseminated intravascular coagulation. This patient was not known for this ulcerative colitis and was first hospitalised for a suspicion of diverticulitis. The admission symptoms were fever, abdominal pain and bloody diarrhoea. The evolution was defavorable under antibiotics and sulfasalazine. The patient was readmitted 5 days after he left hospital, and the diagnosis of UC was based on colon biopsy made during the first hospitalisation. A treatment with methylprednisolone was started and the patient worsened day by day with apparition of toxic megacolon and disseminated intravascular coagulation. Subtotal colectomy was performed for degradation of general status and coagulation factors. Pathological findings confirmed ulcerative colitis with toxic megacolon. Cytomegalovirus inclusions were demonstrated on the colonic specimen and confirmed by PCR. In this report the authors discuss the etiology of toxic megacolon and disseminated intravascular coagulation in ulcerative colitis surinfected by cytomegalovirus. Mortality of these pathologies is high necessitating rapid diagnosis of cytomegalovirus infection by sigmoid biopsy. Management requires immunosupression interruption and ganciclovir therapy, or surgery in unsuccessful medical treatment.