BACKGROUND/AIMS: Intraductal papillary mucinous neoplasms (IPMN) and mucinous cystic neoplasms are included in mucin-producing pancreatic tumors. The reports about IPMN are not uncommon but those about the mucinous cystic neoplasms are relatively few. The aims of this study were to define the natural history of resected mucinous cystic neoplasms of the pancreas and to identify the findings which suggest malignancy. METHODS: The authors retrospectively evaluated the clinical outcomes of 41 patients with mucinous cystic neoplasms who were surgically resected at Asan Medical Center between 1995 and 2004. RESULTS: Women (n=33) were more frequently affected than men (n=8). Thirty three patients (80.6%) had adenoma, 1 (2.4%) borderline malignancy, 1 (2.4%) carcinoma in situ, and 6 (14.6%) invasive mucinous cystadenocarcinoma. The most frequent symptom was abdominal pain (39%). About half of the enrolled patients were asymptomatic. Unilocular type (79%) was more frequent than the multilocular type (21%) on gross morphology. The tumor size of invasive mucinous cystic neopolasms was larger than that of non-invasive mucinous cystic neoplalsms (p=0.01). Abdominal pain was more frequent in invasive mucinous cystic neoplasms (p=0.026). On gross morphology, mural nodules were detected in 4 of 6 patients with invasive mucinous cystic neoplasms. However, they were not detected in any patients with non-invasive mucinous cystic neoplasms. Recurrence developed in none of the 35 patients with non-invasive mucinous cystic neoplasms, however 2 of the 6 patients with invasive mucinous cystic neoplasms died within 5 years. CONCLUSIONS: Clinical predictors of invasive mucinous cystic neoplasms are suggested to be tumor size and abdominal pain. The prognosis of the non-invasive mucinous cystic neoplasms is excellent when curative resection is performed.