Most mucosa-associated lymphoid tissue (MALT) lymphomas are found in the gastrointestinal tract. The most common site is the stomach, whereas colon MALT lymphomas are rare. There are a few reports of simultaneously diagnosed stomach and colon MALT lymphomas. However, diagnosis of primary colonic MALT lymphoma after complete remission of gastric MALT lymphoma is extremely rare. Although the treatment protocol for gastric MALT lymphoma is well established, there is no consensus protocol for colonic MALT lymphoma owing to its rarity. Herein, we report a case of colonic MALT lymphoma incidentally diagnosed 6 months after completion of radiation therapy for gastric MALT lymphoma and treated via polypectomy, with no recurrence for 3 years. (Korean J Med 2016;90:416-420)