RATIONALE: Primary testicular natural killer (NK)/T-cell lymphoma is an extremely rare and highly aggressive lymphoid malignancy. At present, only 20 cases have been reported. PATIENT CONCERNS: A 32-year-old Chinese man complained of discomfort and swelling of his right testicle for 3 months. Physical examination revealed a 10 × 10 × 9.5 cm mass on the right side of the scrotum area. DIAGNOSES: Pathologic evaluation showed effacement of normal testicular parenchymal architecture by small-to-medium-sized lymphoid cells with irregular nuclear profiles, and immunohistochemical studies positively expressed CD2, CD56, cytoplasmic CD3, granzyme B, perforin, and TIA-1. Therefore, the patient was diagnosed with primary testicular NK/T-cell lymphoma. INTERVENTIONS: The patient underwent CHOP (cyclophosphamide (CTX), pirarubicin (THP-ADM), vincristine (VCR), and prednisolone (PDN)) chemotherapy. OUTCOMES: The patient relapsed 5 months after his initial presentation and died after an infection and gastrointestinal bleed. LESSONS: Clinicopathological assessment of this rare case highlights the clinical and pathological features required to diagnose testicular NK/T-cell lymphoma. In addition, it highlights the dismal survival of these patients. We hope it may serve as a reference aiding prompt clinical diagnosis, which can hopefully improve the survival and quality of life of these patients.