We encountered a case of four cysts of intraductal papillary-mucinous tumor in the pancreas, a 25-mm diameter tumor, a 20-mm tumor, and a 10-mm tumor in the pancreatic body and tail, and a 5-mm diameter tumor in the uncinatus process, and the smallest diameter intraductal papillary-mucinous tumor (5 mm) was regarded as an invasive papillary adenocarcinoma, while the other three intraductal papillary-mucinous tumors were adenomas. A 63-year-old asymptomatic male was indicated of the presence of multiple pancreatic tumors by computed tomography during a physical examination. Endoscopic retrograde cholangiopancreatography revealed three cysts (25 mm, 20 mm, 10 mm diameter tumor) in the pancreatic body and tail, and one cyst 5 mm) in the uncinatus process. Cytologic examination of the pancreatic juice determined them as Class V. Based on a diagnosis of malignant intraductal papillary-mucinous tumors, he underwent distal pancreatectomy with removal of the uncinatus process. Pathologically, three cysts in the body and tail of the pancreas were found to be adenomas, but the 5-mm cyst in the uncinatus process was found to be an invasive intraductal papillary-mucinous tumor. The interstitium had been invaded by cancer, and the uncinatus process was the cancer positive surgical margin, and cystological examination of the pancreatic juice through repeated endoscopic retrograde cholangiopancreatography resulted in a class V, so the patient underwent a total pancreatectomy. When diagnosing intraductal papillary-mucinous tumor(s), there is the possibility of incorrectly differentiating between benignancy and malignancy when the diagnosis is based on cyst diameter, as is conventional.