Background: Extranodal natural killer (NK)/T-cell lymphoma, nasal type (ENKTL) is an aggressive disease with poor prognosis, requiring risk stratification. However, the prognosis of ENKTL is not fully defined and needs supplementation. We hypothesised that fasting blood glucose (FBG) may be a new prognostic factor for ENKTL. Methods: We retrospectively analysed 130 patients newly diagnosed with ENKTL. Results: Both univariate analysis and multivariate analysis revealed that FBG >100 mg dl(-1) was associated with a poor outcome. Patients with FBG >100 mg dl(-1) at diagnosis had more adverse clinical features, achieved lower complete remission rates (P = 0.003) and had worse overall survival (P<0.001) and progression-free survival (P<0.001) compared with low-FBG patients. Measurement of FBG was helpful in differentiating between low-risk patients using the International Prognostic Index (IPI) and Prognosis Index for peripheral T-cell lymphoma (PIT) scoring and patients in a different category using the Korean Prognostic Index (KPI) scores with different survival outcomes (P<0.05). Conclusion: Our data suggest that measuring FBG levels at diagnosis is a novel, independent predictor of prognosis in ENKTL and helps to distinguish low-risk patients with poor survival, and this holds true in patients considered low-risk by IPI, PIT and KPI.