A 64-year-old woman was referred for an examination of the upper gastrointestinal (GI) tract. Endoscopy showed an elevated lesion in the duodenum with central depression and multiple white granules. Biopsy specimens revealed lymphoid follicles composed predominantly of centrocytes with scattered centroblasts. The tumor cells were positive for bcl-2. The patient was diagnosed with follicular lymphoma and underwent antibiotic therapy for Helicobacter pylori (H. pylori) infection. The regression of the lesion was obvious. After 5.5 years of follow-up, there has been no evidence of recurrence. This case suggests that H. pylori eradication therapy is effective for treating follicular lymphoma in the duodenum.