Ataxia-telangiectasia (AT) is a rare autosomal recessive disorder that is characterized by progressive cerebellar ataxia, telangiectasia, immunodeficiency, and a predisposition to leukemia/lymphoma. Here we report a rare case of lymphoma of the tongue accompanied by AT. Tumour extirpation was performed and diffuse large B-cell lymphoma was diagnosed following pathologic examination. A whole-body survey showed no other enlarged lymph nodes or tumour. The female patient then received a modified dosage of COPAD (cyclophosphamide, vinblastine, pirarubicin, and prednisolone) plus rituximab to avoid severe complications. As of follow-up after 3 years and 5 months, she remains in complete remission. Patients showing AT need careful surveillance and long-term continuous follow-up.