A 44-year-old Japanese man presented with fever and sore throat. He had a history of refractory chronic sinusitis that did not respond to several years of pharmacotherapy, and underwent endoscopic sinus surgery (ESS) 5 months prior to his presentation, but his symptoms persisted. A biopsy specimen was taken from the right nasal cavity, and extranodal natural killer/T-cell lymphoma, nasal type (ENKTL) was diagnosed. Two years after complete remission was achieved by chemoradiation therapy, he developed hemophagocytic lymphohistiocytosis (HLH) without recurrence of ENKTL. Epstein-Barr virus (EBV)-DNA copy number was relatively high and EBV-infected lymphocytes (CD8 + T cells) were detected in the peripheral blood. Pathological review of the biopsy specimens taken during ESS showed that CD8 + T cells with slightly atypia infiltrating the stroma were EBV positive. These findings suggested that the patient had underlying chronic active EBV infection (CAEBV) that caused the refractory chronic sinusitis, eventually developed into ENKTL, and also caused HLH. Clinicians should consider adult-onset CAEBV in the differential diagnosis of patients with refractory chronic sinusitis.