Extranodal natural killer/T-cell lymphoma, nasal type (nasal ENKTL) is a distinct clinicopathologic entity of lymphoid tumors with variable size and differentiation of tumor cells. Nasal ENKTL is related to infection of the tumor cells with Epstein-Barr virus (EBV) and virtually all cases contain monoclonal episomal EBV DNA and detectable EBV encoded small nuclear RNAs (EBERs). Several clinical factors are known for their relation to the prognosis, but histopathologic prognostic factors of nasal ENKTL have not yet been well established. We evaluated the prognostic value of the longest nuclear diameter of EBER+ tumor cells (NDTC) along with the result of CD30 expression. Twenty two patients with newly diagnosed nasal ENKTL were evaluated regarding clinicopathologic characteristics. NDTC was measured using a computerized image analysis system. The results were expressed as the mean diameter of ≥ 50 cells in a patient. Median of the mean NDTC of the patients was 7.32 μm (5.15-11.27). Patients with larger mean NDTC (≥ 7.35 μm) had a poorer event-free survival (EFS) than those with smaller mean NDTC (<7.35 μm; p = 0.024) and had a tendency of inferior overall survival (OS) (p = 0.08). Patients with CD30 expression had a inferior EFS (p = 0.018) and OS (p = 0.011) compared those without CD30 expression. The NDTC of EBV infected tumor cell and CD30 expression had relation to survival in the current exploratory analysis.