['Localized extranodal natural killer (NK)/T-cell lymphoma, nasal type, commonly has a low or low-intermediate risk of the international prognostic index (IPI), so the IPI has shown inconsistency in predicting prognosis. Thus, we analyzed Ki-67 expression and proposed a new prognostic model including Ki-67 expression for stage I/II extranodal NK/T-cell lymphoma.', 'We studied Ki-67 expression and its relationship with prognosis in 50 patients with extranodal NK/T-cell lymphoma.', 'The patients were dichotomized by the median value: low (<65%) versus high Ki-67 (> or =65%). High Ki-67 was associated with a worse overall survival (OS; P = 0.021) and disease-free survival (DFS; P = 0.044). In multivariate analysis, Ki-67 expression and primary site of involvement were found to be an independent prognostic factor for OS and DFS (P < 0.05). Based on these results, we proposed a new clinico-pathological prognostic model with Ki-67 expression and the primary site of involvement. It showed a high degree of correlation with worse OS and DFS (P < 0.001).'] Is ki-67 expression predictive of prognosis in patients with stage I/II extranodal NK/T-cell lymphoma , nasal type?