Non-Hodgkin's lymphoma (NHL) of the gastrointestinal (GI) tract accounts for 4% to 20% of all NHLs and is the most common extranodal site of presentation. The stomach is the major organ involved by GI lymphoma. Helicobacter pylori infection, immunosuppression after solid-organ transplantation, celiac disease, inflammatory bowel disease, and human immunodeficiency virus (HIV) infection may be risk factors for GI lymphoma. A significant proportion of gastric lymphomas are of low-grade histology and arise from mucosal-associated lymphoid tissue (MALT). Such MALT lymphomas may be associated with H. pylori infection and may undergo complete regression following eradication of H. pylori. Lymphoma of the small bowel, colon, and rectum may also occur, but are less common than gastric lymphoma. Distinct clinicopathologic entities, such as primary intestinal T-cell lymphoma, immunoproliferative small intestinal disease, and multiple lymphomatous polyposis have been described. Surgery, radiation therapy, and chemotherapy have been used in the treatment of GI lymphomas. However, the optimal management of these lymphomas has never been determined by prospective randomized clinical trials. Such trials by cooperative groups are needed to answer many of the vital unanswered questions concerning extranodal lymphomas of the GI tract.