A series of 92 malignant lymphomas of the gastrointestinal tract and mesentery obtained from a population-based registry was studied to assess whether the newly defined concept of mucosa-associated lymphoma has clinical relevance. The cases were grouped according to localization; gastric, intestinal, and mesenteric lymphoma. All cases were reviewed histologically, graded according to the Working Formulation, and reclassified according to the Kiel classification, which was modified to include the categories low- and high-grade mucosa-associated lymphoma. Clinical data, as well as staging and follow-up data, were related to both the original diagnosis and the diagnosis after reclassification. The results showed that the distribution of the types of lymphoma is related to site: centroblastic lymphoma was predominant in the stomach, lymphoblastic in the bowel, and follicular centroblastic-centrocytic in the mesentery. Gastrointestinal lymphoma was disseminated in approximately 50% of the patients at presentation. Survival analysis revealed that classification according to the original Kiel classification and grading according to the Working Formulation provided important prognostic information, whereas introduction of mucosa-associated lymphoma as an entity did not. It was concluded that modification of current classifications to include a separate category for mucosa-associated lymphoma is not useful.