Most primary intestinal natural killer (NK)-cell and T-cell lymphomas (PINKTL) in the Northern Europe are enteropathy-associated T-cell lymphomas, a complication of celiac disease, which is rare in the East. Primary intestinal NK-cell lymphoma is extremely rare and is poorly characterized. We investigated 30 cases of PINKTL from Taiwan with male: female at 2:1, median age at 55.5, 80% with jejunal/ileal involvement, 77% with perforation, 27% with multicentric tumors, and 67% at stage IE. All 7 cases tested for serum IgA anti-tissue transglutaminase were negative. Only 3 (10%) tumors showed enteropathy. Six (20%) were NK-cell lymphoma and 24 (80%) were T-cell lymphoma. The tumor cells in 21/30 (70%) cases were small to medium sized, which correlated with the coexpression of both CD8 and CD56. All tumors expressed at least 1 cytotoxic marker. All 6 NK-cell lymphomas were negative for betaF1, diffusely positive for Epstein-Barr virus-encoded mRNA (EBER), and polyclonal for T-cell receptor gene rearrangement. Five (22%) of the 24 T-cell tumors expressed betaF1, 8 (35%) of the 23 tumors were positive for EBER, and 20 (95%) of the 21 tumors were clonal for T-cell receptor. The overall 1-year survival was 36%. Univariate regression analysis showed that NK-cell lineage, multicentricity, and perforation were associated with poor prognosis. NK-cell lineage (P=0.037) was a poor prognostic factor by multivariate Cox proportional hazard regression analysis. PINKTL in Taiwan is predominantly not enteropathic with a high frequency of perforation, small to medium tumor cell size and cytotoxic phenotype. Primary intestinal NK-cell lymphoma carries a very poor prognosis, and is probably a distinct entity.