Mesenteric vein thrombosis is a rare but severe complication in children requiring splenectomy. We report on a 5-year-old boy with an autoimmune hemolytic anemia who underwent splenectomy because of severe side effects from cortisone therapy. 10 months after splenectomy he presented with signs of a paralytic ileus. Laparotomy showed mesenteric vein thrombosis with hemorrhagic bowel infarction requiring resection of two thirds of the small intestine. An early recognition and thrombolytic or surgical treatment of mesenteric vein thrombosis may reduce the incidence of hemorrhagic infarction, peritonitis, and secondary complications in these patients.