An unusual primary intestinal lymphoma that occurred as a complication of ileal Crohn's disease is presented. Immunohistochemistry confirmed the light microscopic diagnosis of Hodgkin's disease (nodular sclerosing), and characterized a distinct mucosal nodule as a large‐cell anaplastic non‐Hodgkin's lymphoma. This unusual lymphoma developed while the patient was being treated with immunosuppressant medication. The present report is a reminder to clinicians of the possibility of occult lymphoma in ileal Crohn's disease.