Objective:To study the clinical and pathological features of primary NK/T cell lymphoma of testis and to investigate the effective diagnosis and treatment of this disease.Methods:The surgical specimens of two patients with primary NK/T cell lymphoma of the testis were observed by light microscopy

immunohistochemistry and examined by in situ hybridization for Epstein-Barr virus(EBV) RNA and the literature were reviewed.Results:The two patients respectively presented with bilateral and right-side painless testicular enlargement.The neoplastic cells were positive for CD45

CD2

CD56

cytoplasmic CD3(CD3ε)

CD45RO and Granzyme B

while the expressions of CD57

CD20

CD79a

CD30

CK

MPO

TdT

BCL-2 and PLAP were negative.In addition

the EBV RNA was detected in the lymphoma by in situ hybridization.Conclusion:Primary NK/T cell lymphoma of the testis is a rare entity and progressed rapidly.The expression of CD56

CD3ε

cytotoxic granule associated ptoteins and EBV examination by in situ hybridization play an important role in diagnosis and differential diagnosis.