Patients with rheumatoid arthritis, whether treated or not with immunosuppressive agents including methotrexate, have an increased risk of lymphoproliferative disorders. Termed "iatrogenic immunodeficiency-associated lymphoproliferative disorders" in the 2008 World Health Organization classification of lymphoid neoplasms, they include Hodgkin and non-Hodgkin lymphomas. Composite lymphomas are rare, particularly in skin, with none reported in immunodeficiency states. We report the case of a 67 year-old woman with a long history of rheumatoid arthritis, on methotrexate treatment, who developed multiple skin lesions exhibiting a malignant infiltrate displaying both B- and T-cell phenotypes and dual clonal gene rearrangement by polymerase chain reaction, consistent with a cutaneous composite lymphoma. The patient received chemotherapy including rituximab with partial response, but the T-cell component recurred. To the best of our knowledge, this is the first case report of a cutaneous composite lymphoma in a patient with an iatrogenic immunodeficiency representing a dual challenge, diagnostic for the pathologist and therapeutic for the hematologist.