A 39-year-old man infected with human immunodeficiency virus (HIV) was admitted to our hospital because of sudden onset of chest pain. Chest radiography revealed pneumothorax of the right lung. Computed tomographic scans disclosed a 5.8-cm-sized emphysematous bulla in the right middle lobe of the lung. Histologically, the wedge-resected lung showed medium to large atypical cells within the bullous cavity of the Pneumocystis jirovecii pneumonia, without solid mass formation. These atypical cells were confirmed to be large B-cell lymphoma, Epstein-Barr virus–positive and human herpesvirus 8–negative. Therefore, this case was not diagnosed as primary effusion lymphoma, but effusion-based lymphoma arising in an emphysematous cavity of an HIV-infected patient. This type of effusion-based lymphoma has never been reported, and, although rare, it should be noted in order to clinically diagnose this lymphoma.