Fibromas are rare tumors of the nasal cavity, which may result from progressive inflammation or fibroblastic proliferation of the nasal mucosa. The tumors are usually too small to cause symptoms. We present a 47-year-old woman suffering through right nasal obstruction, purulent rhinorrhea and severe headaches for 6 months. A gray-white, smooth-surfaced, gigantic firm mass occupying the right nostril was found in physical examination. Sinus computed tomography revealed 4 x 3 x 3 cm soft-tissue-density mass in the right nasal cavity and right maxillary sinusitis. The huge sinonasal fibroma measuring 4.5 x 3 x 3-cm in the right posterior ethmoid sinus, which was successfully endoscopically resected. The final diagnosis of fibroma was made histologically, according to light microscopy and immunohistochemical stain examinations, which were important for determining the patient's treatment. After endoscopic resection, her initial signs and symptoms were relieved and no recurrence was noted after 2 years of follow up.