Giant cell carcinomas of the lung have been notorious in fulminant clinical courses. Thus, this report describes two exceptionally favorable cases among six cases of giant cell carcinoma of the lung. Their histopathological features are a sharply-demarcated tumor of Stage I, absence of vascular permeation of the cancer cells, prominent lymphoid and plasma cell infiltration in the tumor tissue, and lymph follicle formation in the surrounding tissues. Another case with a Stage II tumor showed the same histopathological findings as the above two cases with the exception of lymphatic permeation of the cancer cells. This patient expired about one year after undergoing an operation. As conventional controls, the remaining three cases with Stage III tumors showed an alveolar extension of tumor cells and vascular permeation. There was a fulminant course after the operation. Notwithstanding similar intervals from their clinical onset to operation in the 4 cases other than Cases 4 and 6, their stages showed considerable variations. Hence, each histopathological feature might have substantiated the different clinical courses following the operation. Electron microscopy of three of the cases indicated double-membrane-bound blisters with intermediate junctions in the bizarre giant cells, and cancer cell differentiation toward both glandular and squamous directions.