From this study I suggest that extramedullary plasmacytoma (EMP) shows several important differences from myelomatosis and solitary myeloma of bone (SMB) which can be summarized as follows: 1. A marked preference for the primary tumor to present in a particular site, namely the upper air passages. 2. A high incidence of metastatic spread to soft tissues. 3. Spread to bone occurs frequently but shows no preference for bones containing active hematopoietic tissue and widespread bone-marrow involvement occurs only occasionally. 4. Prolonged survival may be achieved with therapy for local disease. 5. Vigorous treatment for disseminated disease can be given and may result in longer remissions than those usually seen in myelomatosis. Healing of bone lesions has been observed on several occasions. It is concluded also that SMB constitutes a rather unusual presentation of myelomatosis but is essentially the same disease process.