Two cases of primary pulmonary osteosarcoma are presented. In both cases, chest computed tomography revealed a calcified pulmonary mass and technetium-99m methylene diphosphonate bone scintigraphy showed intense uptake in the pulmonary mass. Primary pulmonary osteosarcoma was suspected on the basis of these radiographic findings. Microscopic examination of tumor specimens obtained by needle biopsy revealed histologic features of osteosarcoma, and this diagnosis was confirmed by postmortem examination of a second specimen in each case. Radiographic and histopathological findings enabled us to diagnose primary pulmonary osteosarcoma, which is one of the rarest types of cancer.