Gastric mucosa-associated lymphoid tissue (MALT) lymphoma has been linked to Helicobacter pylor infection and low-grade gastric MALT lymphoma can completely regress after eradication of H pylori infection. However, duodenal MALT lymphoma is very rare and the relationship with H. pylor infection is still obscure. This case report describes a 76-year-old man who had polypoid mass in the duodenal bulb and was diagnosed as low-grade MALT lymphoma with stage IEA. Eradication of H pylori infection with antibiotics resulted in regression of the gross duodenal lesion. However, 10 months after H. pylori eradication, cervical lymphadenopathy was noticed and excisional biopsy revealed marginal zone B-cell lymphoma despite the regressed state of duodenal lesion. To the bes of our knowledge, this is the first case report of duodenal MALT lymphoma which showed dua clinical response after eradication of H. pylori. (Kor J Gastroenterol 1999;33:287 - 291)