The prognostic nutritional index (PNI), an indicator of nutritional status and systemic inflammation, is associated with survival in several types of tumors. The prognostic value of the PNI in lymphoma remains unclear. The present study aimed to evaluate the prognostic significance of the PNI in patients with extranodal natural killer/T cell lymphoma, nasal type (ENKTL). This retrospective study in two institutions was comprised of 177 patients with newly diagnosed ENKTL. Patients with a combined albumin (g/L) + 5 x total lymphocyte count x 10(9)/l a parts per thousand yenaEuro parts per thousand 45 were allocated a PNI score of 0. Patients in whom this total was < 45 were allocated a score of 1. Patients with a pretreatment PNI score of 1 had more adverse clinical features, lower complete remission rates (p = 0.005), and worse overall survival (OS, p < 0.001) and progression-free survival (p = 0.004) compared with those with a PNI score of 0. Multivariate analysis showed that the PNI (p < 0.001) and tumor mass a parts per thousand yen5 cm (p < 0.001) were independent predictors of worse OS. The PNI was predictive in extranasal disease and nasal disease (both p < 0.05). The PNI could differentiate low-risk patients as classified according to the International Prognostic Index and Prognosis Index for peripheral T cell lymphoma scoring, as well as patients in a different category using the Korean Prognostic Index scores with different survival outcomes (all p < 0.05). The PNI is a powerful predictor of survival in ENKTL. Nutritional status and inflammatory responses at diagnosis might play an important role in survival in patients with ENKTL.