Twenty-seven cases of primary peripheral T-cell lymphomas of the intestine (PTLI) were investigated. Seven patients had histories of malabsorption. The most frequent symptoms at presentation were weight loss, abdominal pain, and acute abdomen. The jejunum was the most common site of lymphoma and multifocal disease was found in 72% of the cases. Twenty-two patients (92%) presented with localized disease confined to the intestine and abdominal lymph nodes, only two patients had generalized disease. According to the pattern of lymphoma infiltration and the morphology of the uninvolved small intestinal mucosa, 21 cases were separated histologically into three categories; 1) enteropathy-associated T-cell lymphoma (EATCL, n = 9) showing predominant intramucosal lymphoma spread and villous atrophy of uninvolved mucosa with high density of intraepithelial lymphocytes (IEL), 2) EATCL-like lymphoma without enteropathy (EATCL-LLWE, n = 5) but with an infiltration pattern similar to EATCL, and 3) T-cell lymphoma without features of EATCL (Non-EATCL, n = 7). Distinctive features of EATCL were the high incidence of malabsorption states, multifocal intestinal disease in all cases, and the high frequency of intestinal recurrences. On frozen sections four of eight PTLI showed the phenotype CD3+ CD4- CD8- HML-1+, which is also expressed on a small subset of normal IEL. The morphologic and immunomorphologic findings suggest that the majority of PTLI is derived from mucosal T lymphocytes. This derivation may be responsible for certain biologic features, such as the preferential spread to and relapse of PTLI at small intestinal sites.