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Extramedullary multiple myeloma is characterized by clonal plasma cell proliferation outside the bone marrow and is associated with an adverse prognosis, particularly when accompanied by high-risk cytogenetic abnormalities. Sinonasal involvement is rare and may present with recurrent epistaxis or unilateral nasal obstruction, creating diagnostic overlap with inflammatory, vascular, lymphoid, and epithelial sinonasal lesions. We report a 54-year-old man with an eight-month history of progressive right-sided nasal obstruction and intermittent epistaxis that became increasingly frequent and refractory to nasal packing. Magnetic resonance imaging showed a right sinonasal mass involving the nasal cavity and maxillary sinus, with septal deviation and no radiological evidence of orbital floor or nasal septal erosion. Endoscopically guided biopsy demonstrated a dense plasma cell infiltrate with mature and atypical forms. Systemic evaluation revealed anemia, multiple lytic skull and humeral lesions, 32% bone marrow plasma cell infiltration, an IgG monoclonal protein with lambda light-chain restriction, and high-risk cytogenetic abnormalities including CKS1B 1q gain, deletion 17p, and deletion 13q. These findings established a diagnosis of high-risk symptomatic multiple myeloma with extramedullary sinonasal involvement rather than a solitary extramedullary plasmacytoma. This case emphasizes that recurrent epistaxis associated with a unilateral sinonasal mass warrants early biopsy and systemic evaluation, particularly when clinical or laboratory features suggest an underlying plasma cell neoplasm.