A high prevalence of nasal lymphoma expressing a T- or natural killer (NK)-cell phenotype (NTCL) with frequent association of Epsteln-Barr virus (EBV) has been indicated in Asians. To Characterize NTCL among the Japanese, the clinlcopathdogic features of 32 cases were evaluated and the casses worn also analyzed for EBV-RNA using an ISH method. Morphologically, 31 cases were Identified by atypical pleomorphic lymphoid infiltrates with polymorphous, anglcentric, and necrotic features. Their lymphoma cells ranged in size from small to large and were mixed in varying proportion from case to case. The other one case showed a monomorphic ‘blastic’ appearance. EBV-encoded small RNA (EBER) was detected in the neoplastic cells of 27 of the 32 cases examined. In the five EBV-negative cases, one was the ‘blastic’ type. Clonal T-cell receptor gene rearrangement was detected in none of seven cases examined. The patients had a median follow-up of 9 months (range, 1 month to 14 years and 11 months). The Kaplan-Meler estimate of overall survival was 49% at 5 years, correlating with clinical stage. These data support the concept that most cases of NTCL are identified as tumors with T/NK-cell characteristics and EBV association, distincity different from other peripheral T-cell lymphomas. Furthermore, the one case of an EBV-negative ‘blastic’ variant appears not to fit well Into the pleomorphic category but more closely resembles the pathologic features of extranasal angiocentric lymphoma with lymphoblastold appearance. This study also showed no clear difference in clinical aspects other than the original site or in prognosis, between NTCL and extranasal angiocentric lymphomas despite the higher incidence of EBV association and the tendency for that peculiar anatomical site to be restricted to the former group.