The majority of primary testicular lymphomas are of B-cell type. Other primary lymphomas are rarely encountered in the testes. Natural killer (NK)/T-cell lymphomas of nasal type are aggressive extranodal lymphomas associated with Epstein-Barr virus infection that are usually encountered in the upper aerodigestive tract. They also occur in the skin, soft tissue, and colon. Primary testicular NK/T-cell lymphomas are rarely reported. We describe the case of a 66-year-old Korean man who presented with right-sided painless testicular enlargement and underwent radical orchiectomy. Histologic examination revealed an angiocentric and angioinvasive infiltrate of medium to large tumor cells with moderately abundant pale pink cytoplasm and folded and indented pleomorphic nuclei. Paraffin immunohistochemical studies showed positivity of the tumor cells for CD45, TIA-1, granzyme B, CD56, and CD3 epsilon. In situ hybridization showed diffuse positivity for Epstein-Barr virus-encoding RNA. The results of gene rearrangement studies for the gamma chain of the T-cell receptor were negative. The results of paraffin immunohistochemical studies for CD20, CD8, CD45RO, beta f1, and ALK-1 were negative. An extensive workup showed no evidence of lymphoma outside the testes. We report a rare case of primary testicular NK/T-cell lymphoma of the nasal type of true NK-cell origin.