Intestinal intraepithelial lymphocytes are non-organized lymphoid populations that are composed of heterogeneous subsets with diverse ontogeny and phenotypes, and the differential diagnosis is crucial. A 43-year-old male patient underwent an emergency laparotomy due to a perforated mass of the terminal ileum. A right hemicolectomy plus small bowel resection was performed. Histopathological examination showed medium to large cells with vesicular nuclei, including marked nucleoli with large, colorless cytoplasm. No signs of celiac disease were found in the adjacent mucosa. The tumor cells were immunohistochemically CD45+, CD3+, CD4+, CD8+, CD56+, Pan-Cytokeratin-, CD20-, CD79a-, CD5- and CD30-. Endomysial antibody and antigliadin antibody, IgM and IgG tests; and anti-Ebstein Barr virus latent membrane protein all proved negative. Finally, the histopathological diagnosis of tumor mass was natural killer-like T-cell lymphoma. Primary intestinal cytotoxic natural killer-like T-cell lymphoma is a rare entity, which is difficult to distinguish from other T-cell lymphomas. In addition to microscopic evaluation, immunohistochemical analysis and serological tests are essential to reach a definitive diagnosis.