We retrospectively studied 19 cases of nasal NK/T-cell lymphoma for various potential prognostic factors and performed real-time quantitative polymerase chain reaction for Epstein-Barr virus (EBV) viral load in tumor tissue. Patients with a low EBV viral load (<1 copy per cell) more frequently survived for more than 2 years compared with patients with a high EBV viral load (>/=1 copies/cell) (7/7 vs 3/9; P = .014; Fisher exact test). Furthermore, the patients with low EBV viral loads had a better overall survival than patients with high viral loads (50% accumulative survival: not reached vs 4-5 months; Kaplan-Meier survival analysis; P = .049). In contrast, the overall survival of the patients did not correlate with the extent of lesion, age, stage, necrosis, histologic subtypes, CD56 expression, or angiocentric or angiodestructive growth pattern. Our findings suggest that the EBV viral load in tumor tissues is a useful indicator for predicting outcome of nasal NK/T-cell lymphoma.