Lymphomas of mucosa-associated lymphoid tissues (MALT) are localized in organs containing lymphoid tissue in normal subjects (lung) or in organs frequently involved by inflammatory lesions (stomach, salivary glands, thyroid...). In the MALT, lymphoid tissue comprises B and T lymphocytes. Lymphomas of the MALT have been well defined in the gut. Isaacson has proposed a classification of these primary gut lymphomas, distinguishing between B, the most frequent, and T lymphomas, and between low and high grade of malignancy. MALT lymphomas have common morphological characteristics and a particular behaviour: they are localized in their initial site for a long time. Prognostic factors include low histological grade of malignancy and the possibility of a complete surgical resection.