OBJECTIVE: Pancreatic neuroendocrine tumors expressing serotonin (carcinoid tumors) account for a small portion of pancreatic neuroendocrine tumors. The purpose of this study was to describe cases of small serotonin-producing pancreatic neuroendocrine tumors associated with pancreatic duct obstruction. CONCLUSION: Serotonin produced by pancreatic neuroendocrine tumors can induce fibrosis and pancreatic duct obstruction. Pancreatic neuroendocrine tumors should be considered when CT shows a small hypervascular mass associated with upstream pancreatic duct dilatation or atrophy. Evidence of small pancreatic neuroendocrine tumors should be sought in cases of idiopathic pancreatic duct stenosis.