Primary pulmonary malignant lymphoma is a rare disease that is thought to belong to a category of malignant lymphomas arising from mucosa- or bronchus-associated lymphoid tissue (MALT or BALT). We encountered 3 cases of primary pulmonary malignant lymphoma, Case 1: In a 51-year-old male, an abnormal shadow was detected in chest radiography in the right S9 after an operation for thyroid carcinoma. A right lower lobectomy was performed. The diagnosis was malignant lymphoma (marginal zone B-cell lymphoma). Immunohistochemical staining for IgM gave a positive result. Case 2: Multiple nodular shadows were noted in both lungs of a 55-year-old man after a bout of pneumonia. Video-assisted thoracoscopic surgery was performed, and the diagnosis was malignant lymphoma (marginal zone B-cell lymphoma). Gene analysis revealed rearrangement of a heavy chain gene. Case 3: An abnormal shadow was seen in the chest radiograph of a 60-year-old man. He was treated by right upper and middle lobectomy. The diagnosis was Hodgkin's disease, nodular sclerosing type. Chemotherapy was given after surgery and the patient is now alive without recurrence. As the pulmonary malignant lymphoma was difficult to diagnosepreoperatively, it was necessary to resect the mass for diagnostic purposes. The prognosis of a resected solitary lesion in the lobe was good. Therefore lobectomy was performed as the treatment of choice. Systemic chemotherapy is performed for the diffuse type of pulmonary lymphoma.