Aims To report a case of small-cell (indolent), nasal-type extranodal natural killer (NK)/T-cell lymphoma in a 64-year-old Māori male with chronic sinusitis, emphasising its diagnostic challenges and management with its exceedingly rare nature. Methodology The patient presented with a two-year history of nasal obstruction and refractory chronic sinusitis, undergoing bilateral functional endoscopic sinus surgery for nasal polyposis. Initial histology was suggestive of EBV-driven chronic sinusitis. Persistent symptoms despite systemic steroid therapy necessitated repeat surgery, with histopathological review by local and international experts. Results Histopathology demonstrated a dense submucosal lymphoid infiltrate with small-cell morphology, focal atypia, and EBV positivity. Elevated EBV viral loads were observed, but imaging with magnetic resonance imaging (MRI) and positron emission tomography (PET) showed no nodal spread or systemic involvement. The lymphoma was classified as a low-grade variant of nasal-type NK/T-cell lymphoma, an entity not yet recognised in the current World Health Organisation (WHO) classification of lymphoid malignancies. Multidisciplinary team (MDT) consensus was to proceed with involved field radiotherapy, and the patient demonstrated significant response with systemic steroids and completed 50 Gray in 20 fractions. He remains asymptomatic, working full-time, and has no B-symptoms. Conclusion This case illustrates the importance of considering lymphoma in refractory chronic sinusitis. The small-cell variant’s indolent behaviour differs sharply with the typically aggressive nature of this lymphoma subtype. Accurate diagnosis requires expect histopathological confirmation and MDT discussion. Awareness of this exceedingly rare presentation is essential to avoid delays in diagnosis and optimise patient outcomes.