The clinical presentation of intraductal papillary mucinous tumor (IPMT) of the pancreas is characterized by chronic or recurrent attacks of abdominal discomfort often in association with low level pancreatic enzyme elevations. The episodes of pancreatitis due to IPMT of the pancreas are usually mild in severity. Recently, however, we experienced a case of IPMT of the pancreas causing severe acute pancreatitis with a protracted course in a 65 year-old woman. Initially, she presented with pancreatic ascites and hyperenzynemia without duct ectasia and mucus extrusion through the papillary orifice. Refeeding caused aggravation of hyperenzynemia and abdominal pain. The 4th follow-up abdominal computed tomography taken about 2 months after admission only revealed marked dilatation of the main pancreatic duct. Distal pancreatectomy disclosed IPMT, combined type and carcinoma in situ histologically. The patient has been followed for 2 years after operation with an uneventful clinical course. We herein report a case of IPMT of the pancreas with an unusual presentation.