淋巴瘤是起源於淋巴組織的惡性腫瘤，又可分為何杰金氏及非何杰金氏淋巴瘤。在台灣非何杰金氏淋巴瘤的發生率遠高於何杰金氏病，約為9:1。除了淋巴結腫大以外的表現以腸胃道侵犯最為常見，其中主要以十二指腸表現為主的淋巴瘤預後最佳。我們報告一位70歲女性因為腹痛而接受上消化道內視鏡檢查，於十二指腸第二段意外發現許多白色斑點，切片證實為濾泡性淋巴瘤，經血液腫瘤科和放射腫瘤科會診後採取局部放射線治療，經過4年內視鏡切片和電腦斷層追蹤並無復發，因常規上消化道內視鏡常易輕忽這些以內視鏡表現位主但卻是早期發現治療效果極佳的疾病，故提出此患者診斷和治療方式及後續追蹤經驗。

Follicular lymphoma (FL) is one of the most common types of non-Hodgkin lymphoma (NHL), and the gastrointestinal tract is the most commonly involved extranodal site. Primary duodenal FL (DFL), which mainly involves the second portion of the duodenum and has an excellent prognosis, is an unusual entity with only a few reported cases in the literature. The first reported case of primary duodenal follicular lymphoma was in 1997, and we could not find similar case reports in Taiwan. We report the case of a 70-year-old woman who underwent esophagogastroduodenoscopy due to mild, persistent epigastric pain. Endoscopic findings revealed numerous whitish and small submucosal nodules scattering diffusely in the second and third portions of the duodenum. The biopsy of these lesions revealed a pathological result consistent with FL. This elder patient with gastrointestinal symptoms was referred to the Oncology department for further management, and radiation therapy was chosen for treatment. Neither lesion aggregation nor lymphadenopathy was noted during the 4-year follow-up period. In conclusion, this was an uncommon case of DFL responding favorably to radiation therapy and having an excellent prognosis. However, due to the lack of cases reported in Taiwan, further studies are needed to clarify the disease's characteristics, therapeutic approach, and prognosis.