We performed a clinical analysis on 8 patients with primary follicular lymphoma in the duodenum taken from among 26 cases of primary gastrointestinal malignant lymphoma treated in our division. The median age was 60 years (range 48 to 82 yr). The ratio of males to females was 4:4. The chief complaints were no symptoms in 4 cases, heartburn in 2 cases, lower abdominal pain in 1 case, and back pain in 1 case. All patients were in clinical stage I EA. Gastroendoscopic findings showed multiple whitish granules around the ampulla of Vater in all patients. Involvement of the site in 6 cases was only located at the second portion; lesions in the other 2 cases were located at the second portion, and at the third portion or fourth portion, respectively. A histological study showed follicular lymphoma grade 1, and an immunohistological study demonstrated that the lymphoma cells were positive for CD79a, CD10, CD20, and bcl-2. Five patients were positive for the FISH analysis fusion signal of IgH/bcl-2 genes. Rituximab with CHOP therapy was performed for 7 patients. Seven patients are currently alive, and one died of uterine cancer. At the medium-term 39 month-follow-up, 7 patients were in complete remission, and 1 patient was in partial remission. Rituximab with CHOP (CVP) therapy is a possible treatment for primary follicular lymphoma in the duodenum. Further consideration of appropriate therapy for this disease might be necessary.