We report six cases of primary pulmonary lymphoma in which a gene-rearranged band was shown by Southern blot analysis of transbronchial or surgical biopsy specimens. The cases were 3 mens and 4 women with an average age of 59.6, who had abnormal pulmonary shadows on chest X-ray. Two cases had Sjögren's syndrome and one case had monoclonal gammopathy (IgM-lambda type). Histopathologic and immunologic examination revealed diffuse infiltration of small lymphocytes (B-cell type) in all cases, and histological features of lymphoepithelial lesion or lympho-cytic interstitial pneumonia (LIP) in three cases. CT revealed an ill-defined margin, air-space consolidation, and air-bronchogram in all cases. A CT-angiogram sign was apparent in 2 cases. In all cases, Southern blot analysis of the tissue obtained from transbronchial or surgical biopsy revealed a gene re-arranged band, supporting the diagnosis of primary pulmonary lymphoma. We infer that an ill-defined margin, air-bronchogram and air space consolidation on CT were associated with the histopathological features of primary pulmonary lymphoma.