OBJECTIVE: To investigate the role of radiation therapy in the comprehensive treatment of IE-IIE stage nodal extranodal NK/T-cell lymphoma and the prognostic factors affecting patient survival. METHODS: A retrospective analysis of 177 patients, 127 males and 50 females, aged 17-80 years (median 44 years), admitted to Sun Yat-sen University Cancer Hospital from 1990 to 2006. 138 patients were in stage IE, 39 in stage IIE, and 60 in extensive local invasion. The stage-adjusted International Prognostic Index (mIPI) scores of 0, 1, 2 and 3 were 42.9%, 34.5%, 11.9% and 1.7%, respectively. 165 patients received the first course of chemotherapy, of which 37 received chemotherapy alone (median 4 cycles) and 128 received chemotherapy (median 3 cycles) + radiotherapy (median dose 52 Gy); 12 patients received the first course of radiotherapy, of which 6 received radiotherapy alone (median dose 58 Gy). median dose of 58 Gy) in 6 cases and radiotherapy (median dose of 54 Gy) + chemotherapy (median of 5 cycles) in 6 cases. RESULTS: The overall remission (CR+PR) rate after the first course of chemotherapy was 60.8%, and the overall remission rate after receiving radiotherapy was 83.8% (P<0.01). The median follow-up time of surviving patients was 47.5 months. The 5-year overall survival (OS) and progression-free survival (PFS) rates for the entire group were 46.2% and 36.8%, respectively. Patients receiving radiotherapy had better local control (80.9%) than those receiving chemotherapy alone (50%, P<0.01), with 5-year OS of 53.4% and 18.3%, and 5-year PFS of 45.0% and 10.9%, respectively (both P<0.01). Patients with disease remission (CR+PR) versus no remission (SD+PD) after the first course of chemotherapy had significantly better 5-year OS and PFS with radiotherapy than those with chemotherapy alone (P<0.01 for both). Age <60 years, female, no extensive local invasion, PS (ECOG) <2 score, remission after the first course of chemotherapy, and receiving radiotherapy were favorable prognostic factors for OS, and female, mIPI <2 score, remission after the first course of chemotherapy, and receiving radiotherapy were favorable prognostic factors for PFS. CONCLUSION: Radiation therapy significantly improved tumor remission, local control, and survival in early-stage extranodal nasal NK/T-cell lymphoma compared with chemotherapy, and also showed significant efficacy in patients with local tumor stabilization or progression after chemotherapy. Radical radiation therapy is the treatment of choice for early-stage nasal NK/T-cell lymphoma, and the efficacy of combination therapy for poor prognosis cases remains to be improved.