Background: Extranodal NK/T-cell lymphoma, nasal type is a locally invasive tumour, including ulcerative and necrotic lesions, preferentially originating in the nasal cavities and sinuses. It can be frequently confused with a localized form of granulomatosis with polyangiitis (GPA, formerly known as Wegener's granulomatosis), which affects the upper respiratory tract through the same kind of destructive lesions. Case presentation: A 39-year-old man with bilateral nasal obstruction, purulent rhinorrhea, oro-pharyngeal pain, anosmia, halitosis, severe upper dysphagia, and nasal dysmorphism was referred for rheumatologic reevaluation. Over 2 years of evolution, multiple nasal biopsies were performed showing chronic granulomatous inflammation and necrosis, with no malignant cells. Although antineutrophil cytoplasmic antibodies test was negative, the patient was diagnosed with GPA and treated with corticosteroids and immunosupressors. The disease worsened progressively, leading to destructive lesions of the naso-sinusal region. A new biopsy revealed this time atypical lymphoid cells. Upon immunohistochemical characterization, the atypical cells showed CD3+ and granzyme B+ phenotype. In addition, Epstein-Barr virus was identifi ed. Thereafter, nasal type of extranodal NK/T-cell lymphoma was confi rmed. The patient underwent chemotherapy regimen with favourable outcome. Conclusion: When evaluating a patient with destructive midline lesions, clinical suspicion for extranodal NK/T-cell lymphoma, nasal type is necessary. Multiple, large enough biopsies and immunohistochemistry studies are helpful for diagnosis.