Summary1. Three cases of acute enterocolitis (Crohn's disease) are presented.2. A discussion of this disease is undertaken, with special regard to aetiology, pathology, treatment and prognosis.3. On the pathological side, the presence of hypertrophy of the mesenteric lymph nodes is emphasized. It is pointed out that in their absence acute Crohn's disease should not be diagnosed.4. The difficulties of preoperative diagnosis are stressed.5. Conservative treatment of the affected bowel is advised.6. Prognosis of the acute disease is shown to be good.