We studied 42 intestinal T-cell lymphomas (ITLs) to establish a simple and reproducible classification. The ITLs were classified into pleomorphic small cell (n = 3), monomorphic medium-sized cell (n = 10), pleomorphic medium and large cell (n = 17), immunoblastic (n = 1), and anaplastic large cell (n = 9) lymphomas. Two cases were unclassifiable. Overlapping histologic features were noted between some cases and also within the same tumor and between multiple lesions of the same patient. Histologic evidence of enteropathy was present in most cases. The ITLs expressed cytoplasmic CD3 and antigens associated with cytolytic function (TIA-1, granzyme B), but not CD4 and CD5. Six of the 10 monomorphic medium-sized cell lymphomas were CD56+ T-cell lymphomas. Because of the histologic heterogeneity in some ITLs, we suggest a classification system with 2 main categories: (1) small to medium-sized cell, comprising pleomorphic small and monomorphic medium-sized cell lymphomas; and (2) large cell, comprising the remaining subtypes. The differential diagnosis includes B-cell lymphomas, tumors of histiocytic origin, anaplastic carcinoma, and malignant melanoma.