Chronic intussusception, defined as intussusception continuing over 14 days, is rare in children. We herein report a case of chronic ileocolic intussusception caused by the transmural infiltration of diffuse large B cell lymphoma in a 14-year-old boy. The patient had been suffering from anorexia and intermittent abdominal pain for 5 weeks, during which his body weight decreased by around 7 kg. Upon admission to our hospital, ultrasonography and enhanced computed tomography (CT) of the abdomen showed ileocolic intussusception. A retrospective examination of abdominal CT led us to suspect that the intussusception had initially appeared 5 weeks before admission, presumably coinciding with the beginning of the patient's abdominal symptoms. Since hydrostatic reduction was unsuccessful, laparotomy was performed, which showed unreducible ileocolic intussusception with a marked edematous ileum and mesentery. Ileocecal resection without lymph node dissection was carried out, and a histological examination of the resected specimen revealed the transmural infiltration of diffuse large B-cell lymphoma of the terminal ileum. The patient's postoperative course was uneventful, and adjuvant chemotherapy was administered. This case illustrates the diagnostic challenges of confirming 'chronic' intussusception in older children.