A 79-year-old man with a history of tuberculosis was found to have chronic empyema in the right lung and was diagnosed with malignant diffuse large-cell lymphoma (Ann Arbor stage IIE). After completion of one course of rituximab plus cyclophosphamide, pirarubicin, vincristine, and prednisolone (R-CHOP) chemotherapy, the patient developed lung abscess and sepsis caused by Streptococcus intermedius. This condition was treated with antimicrobial agents, and chemotherapy was resumed. After the second course, the chemotherapy regimen was continued without prednisolone, and after administration of the third course, a chest wall mass was found in the right lung. An acid-fast bacillus smear test of the abscess aspirate was positive, and Mycobacterium tuberculosis was detected in a polymerase chain reaction assay, leading to a diagnosis of perithoracic tuberculosis. Chemotherapy for the lymphoma was discontinued, and treatment with four oral antitubercular agents was started. This treatment led to remission of perithoracic tuberculosis. In Japan, tuberculous scar and chronic empyema are relatively common findings, and relapse of tuberculosis should always be considered for patients with these findings during chemotherapy and immunosuppressive therapy.