Plasma cell neoplasms have been classified as multiple myeloma, solitary plasmacytoma, and extramedullary plasmacytoma. The solitary plasmacytoma of the maxilla is a rare condition that focuses solely on myelomatous tissue and is not disseminated to other parts of the skeleton. Some lesions appear to be benign and do not recur after complete removal, while others are locally invasive. The dense plasma cell infiltration that commonly is associated with inflammatory lesions within the oral tissues makes diagnosing plasmacytoma at this site problematic. This article presents a case of solitary plasmacytoma in the maxilla. Radiographic examination revealed an osteolytic lesion over the right maxillary bone, invading the maxillary sinus. A CT scan showed that the tumor mass occupied the right maxillary sinus and the lateral wall of the nasal cavity. The tumor cells were composed of densely packed, round, polygonal cell structures that were scattered in relatively sparse stoma. The neoplastic cells had a large, single eccentric nucleus, resembling typical plasma cells. The clinical, histopathological, and radiological features of solitary plasmacytoma are discussed.