18 Background: MALT (mucosa-associated lymphoid tissue) lymphoma usually occurs in stomach but various MALT organs can be afflicted including salivary glands, ocular adnexa, lung, intestine and thyroid. In this study, we aimed to evaluate the prevalence and characteristics of gastric MALT lymphoma with multi-organ involvement. Methods: We retrospectively analyzed a total of 174 consecutive patients who had been diagnosed with gastric MALT lymphoma at Seoul St. Mary’s Hospital from January 2009 to May 2018. Clinical data were obtained from the medical records. At the time of diagnosis, neck, chest, abdominal CT, PET-CT and bone marrow biopsy were performed for the purpose of staging work-up. Organ involvement was identified by biopsy. Results: Nine out of 174 (5.2%) gastric MALT lymphoma patients were found to have multi-organ involvement. Three patients had biopsy proven lymphoma at lung, two patients had colon involvement, and two patients had ocular involvement. A patient with involvement at small bowel and duodenum were found, respectively. Seven patients were examined for Helicobacter infection. Two of them were positive for H. pylori infection and received eradication treatment. Except one patient treated with palliative care, eight patients underwent chemotherapy, in which two of them received additional radiation therapy and other two patients underwent bone marrow transplantation. Except one patient died of pneumonia during chemotherapy and one patient underwent palliative treatment, 7 patients had maintained complete remission. Conclusions: The overall prevalence of gastric MALT lymphoma with multi-organ involvement was 5.2%. The result suggests that the gastric MALT lymphoma patients require a careful investigation of other MALT organs. [Table: see text]