Primary non-Hodgkin lymphoma (NHL) of the nasal cavity is a rare neoplasm. They account for about 0.17-2% of all cases of NHL and 5.8% of all malignant neoplasms of the sinonasal region in adults. A 37-year-old male patient presented with left-sided nasal obstruction and headache which appeared a couple of weeks before the admission. Nasal examination revealed a massive polyposis. After medical therapy with corticosteroids, neither the polyposis nor his complaints showed regression; thus, he underwent a nasal polypectomy operation. Biopsy results indicated an inflammatory nasal polyp. Two weeks later, a rapidly progressive facial swelling, especially in the left periorbital area and blurred vision occurred. Second biopsy, which was also taken from the left nasal cavity suggested again an inflammatory nasal polyp. To rule out any possible malignancy, a third biopsy was conducted in the left maxillary sinus which indicated T/NK cell lymphoma of the sinonasal tract.