We report a case of sinonasal lymphoma with a natural killer (NK) phenotype. This 40-year-old man was admitted to our hospital because of left nasal obstruction. Physical examination and computed tomography of the skull revealed a tumor in the left nasal cavity and maxillary sinus. Histopathological examination revealed a diffuse proliferation of pleomorphic lymphoid cells. Imprint cytology showed that tumor cells contained some azurophilic granules, and expressed CD2, CD8, CD16, CD56 and HLA-DR antigens with little expression of other lymphoid or myeloid markers. Southern blot analysis revealed germline configuration for immunoglobulin heavy chain and T-cell receptor genes. These findings indicated that these cells were in fact NK cells. The patient's enlarged pancreas was also involved by lymphoma and the pattern of involvement simulated that seen in primary pancreatic lymphoma. Ulcerative colitis (UC) was also present, a rare finding in this disorder.