Plasmacytomas are rare tumors that often appear in the head and neck region and are characterized by a monoclonal proliferation of plasma cells. On both clinical presentation and pathologic examination these tumors may be confused with more common tumors of the head and neck. The purpose of this article is to review our experience with these rare neoplasms, with emphasis on clinical, pathologic, and therapeutic features. On retrospective chart review, we identified 20 patients with the diagnosis of plasmacytoma of the head and neck region at the Cleveland Clinic Foundation between 1976 and 1993. Records were reviewed with regard to initial symptoms, location of the neoplasm, diagnostic evaluation, treatment modalities, and survival. Of the 20 cases we identified, the tumor arose in the sinonasal/nasopharyngeal region in 11 (55%). Two cases (10%) represented medullary plasmacytomas, arising in the clavicle and presenting as supraclavicular masses. The mean follow-up was 60.2 months (range 6 to 131 months). In 15 of the 20 cases, immunohistochemistry staining for immunoglobulin light chain production was conducted. One of the two cases (50%) classified as medullary plasmacytoma demonstrated conversion to multiple myeloma, whereas only 2 of 18 cases of extramedullary plasmacytoma (11%) converted to multiple myeloma. The primary modality of treatment was radiation therapy with typical doses of 4500 to 6000 cGy. Kaplan-Meier survival estimates demonstrated 95% survival at 1 year, 82% survival at 5 years, and 10-year estimated survival of 72%. Plasmacytomas of the head and neck region are rare and on initial evaluation must be distinguished from multiple myeloma. The diagnostic evaluation includes appropriate radiologic and pathologic studies including immunohistochemistry. Despite the typical presentation as a locally destructive tumor, plasmacytomas are highly radiosensitive, and 70% to 80% survival may be obtained with the use of radiotherapy. Patients with plasmacytomas require long-term follow-up to detect conversion to multiple myeloma.