The association of malignancy with autoimmune rheumatic diseases has been a subject of investigation. It has been shown that there is increased risk of malignancies, mainly non-Hodgkin lymphoma, in patients with autoimmune disorders. There is scarcity of data about malignancy in juvenile idiopathic arthritis (JIA). We report the occurrence of anaplastic large cell lymphoma in a patient with systemic onset juvenile idiopathic arthritis treated with low dose methotrexate (MTX). A relationship between MTX treatment and the occurrence of lymphoma in autoimmune diseases has been suggested. The hypothesis that MTX has a role in the aetiology of lymphoproliferative disorders is supported by the observation of spontaneous remission of lymphoma in few cases on cessation of MTX therapy. However, systemic onset juvenile idiopathic arthritis patients receiving MTX must be periodically examined for the development of lymphoproliferative disorder especially if the disease is difficult to control or patient develop new symptoms on therapy.