Primary solitary extramedullary plasmacytoma is a malignant neoplasm characterized by the monoclonal proliferation of plasma cells outside the bone marrow. The tumor rarely occurs in the sinonasal tract, accounting for about 4% of all non-epithelial sinonasal tumors. Herein, the authors describe a rare case of sinonasal extramedullary plasmacytoma in a 33-year-old man who presented with a 3-month history of progressively increasing nasal mass, causing obstruction. A CT scan showed a soft tissue mass measuring 5*8*3 cm in the right and left nasal cavities, obstructing the nasal airway. The mass extended to the right maxillary sinus. Histopathology and immunohistochemical tests confirmed it to be plasmacytoma. Lymphomas with prominent plasmacytic differentiation and multiple myeloma workups were negative. The patient initially refused treatment. After counseling, the patient consented to undergo surgery and later radiotherapy treatment. At one-year follow-up, the patient is disease-free with no signs of recurrence. Plasmacytomas are either medullary or extramedullary neoplasms. The latter are extremely rare tumors, more commonly presenting in the submucosal tissue of the upper respiratory tract. A mass or swelling causing nasal or pharyngeal symptoms is by far the most common presentation of this entity in the head and neck region. Because these lesions are radiosensitive, radiotherapy is a recommended treatment approach. Further studies are needed to better understand the prognosis and effective treatment regimens.