BACKGROUND/AIMS: Neuroendocrine tumors (NET) of the pancreas are rare. Its prognosis is better than pancreas adenocarcinoma due to the slow growth, however, malignant NET of the pancreas are observed. The purposes of this study were to evaluate the clinical characteristics and to find the predictive factors of NET which are associated with malignancy and survival. METHODS: We retrospectively evaluated the clinical outcomes of 122 patients with NET of the pancreas who were pathologically diagnosed at Asan Medical Center between 1990 and 2006. RESULTS: Mean age of the patients was 48.9+/-14.0 years and there was no gender predilection. The major clinical manifestations were abdominal pain (44.0%) in non-functional tumor, neuroglycopenic symptoms (100%) in insulinoma and diarrhea (60%) in gastrinoma. Tumor size ranged from 4 to 140 mm (average 29.8+/-23.22). Ninety cases (73.8%) were classified as benign tumors and 32 cases (26.2%) as malignant. In multivariate analysis of clinical characteristics, large sized tumor (>20 mm, p=0.001) was confirmed as sole independent factor to predict malignant NET. Surgical resection was performed in 114 patients. All patients with benign NET are still alive without recurrence. Six out of 32 patients with malignant NET died at an average 40.3 months after diagnosis. The factors indicating favorable outcome were small size of tumors (p=0.046), resection of primary tumor (p=0.000), absence of lymph node invasion (p=0.0116) and distant metastasis (p=0.0005). CONCLUSIONS: Large NET of the pancreas, regardless of their functioning status, were more likely to be associated with malignancy and predictor of worse survival.