A review of the literature shows that osteogenic sarcoma is not rare, but the pathologic changes of this disease have not clearly reported yet. It is the purpose of this report to describe the pathohistogenetic changes with the clinical aspects in an autopsy case of osteogenic sarcoma. An adult man, 23 years of age, was admitted to the Hiraki Modical Clinic of the Okayama University Hospital, on August 24, 1953, complaining of chest ache and haemoptoe. The x-ray examination of the chest at that time showed base ball-sized, hard, lobulated masses in the both lungs. The pathological diagnosis was osteogenic sarcoma metastasized in both lungs from the right hemural tumor which amputated in a lower third of the right hemur four years ago. The average size of the tumors in lungs was 5-4 cm in diameter. They were usually nonencapsulated, and the cut surface was solid, firm, and grayish-white. Microscopically, there were two types of the histogenetic origins in tumors of the lung. The first histologic form, which is designated here as the "osteogenic cell sarcoma", showed the following characteristics. Microscopically, the component cells were fairly uniform and generally identical with osteolytic cells in various stages of fetal histogenetic cycles of the bone. There were some areas wherein the neoplastic cells showed atypical orientation and the nuclei were large and slightly dark. Mitoses and neoplasmic giant cells were found occasionally. In many neoplasmic cells the various courses of hyalinisation, carcification and osification were recognized. The second histologic form, which is labeled here as the "chondroblastic cell sarcoma", showed the following characteristics. Microscopically, neoplasmic tissues exhibited the chondroblastic cells, which made it possible to translate to osteolytic cells occasionally in some neoplasmic circumstances, and they were consisted of pleomorphic giant cells with the polymorphic cytoplasmas and numerous mitotic figures. As mentioned above, hyalinisation, carcification and osification were also found graduately in the cytoplasmas of such chondroblastic cells as osteolytic cells. In result of histologic examination, this case was malignant osteogenic sarcoma which showed extensive metastases in both lungs within five years.