Intraductal papillary mucinous tumors of the main pancreatic duct are often considered to be premalignant or malignant, and therefore surgical resection is recommended. We report two autopsy cases of intraductal papillary mucinous tumor of the pancreas following long-term observation. The first patient was an 84-year-old man with early gastric cancer treated by endoscopic mucosectomy. The second patient was a 77-year-old man with hepatocellular carcinoma treated by percutaneous pure ethanol injection and transarterial embolization. In both patients, endoscopic retrograde pancreatography showed a diffusely dilated main pancreatic duct, with intraductal filling defects expressing mucus, as well as dilated side branches. Obvious intramural nodules were not detected. Due to their advanced age and personal requests, both patients were managed conservatively and followed nonoperatively. In the first patient, serial pancreatograms showed progression of the pancreatic duct dilatation. Both patients died of gastric cancer, the first patient 7(1)/(2) years and the second, 10 years after first presentation, respectively. Autopsies revealed extensive intraductal papillary adenoma throughout the dilated mucus-filled main pancreatic duct. However, there was no evidence of progression to adenocarcinoma. Based on these observations, we suggest that, in patients with intraductal papillary mucinous tumor of the pancreas without obvious intramural nodules, even if the tumor is in the main pancreatic duct, pancreatectomy may not be mandatory, particularly in the elderly.