A case of T-cell type malignant lymphoma of the lung was reported. A 69-year-old woman was referred to our institute because of an abnormal shadow on the chest roentgenogram. She was symptom-free, and physical examination showed no abnormalities. Her laboratory tests were within normal limits. The chest roentgenogram showed a well-defined, nodular density in the left lower lung field without air bronchogram. She underwent a left lower lobectomy and a mediastinal lymphnodes dissection. This disclosed an elastic hard nodule, 2 cm in diameter, without pleural invasion. Pathologically the tumor was diagnosed as malignant lymphoma of T-cell type without regional lymphnode involvement. She is doing well without any sings of recurrence for one year after the operation.