Background/Aims: Long-term patency of pancreaticogastrostomy remains unclear. The purpose of this study is to clarify the long-term patency of pancreaticogastrostomy based on change in the main pancreatic duct diameter. Methodology: Seventeen of 33 patients who underwent pancreaticogastrostomy in our institution were divided into 2 groups according to the preoperative diameter of main pancreatic duct: the non-dilated group (phimain pancreatic duct less than or equal to4mm, 11 patients) and the dilated group (phimain pancreatic duct greater than or equal to5mm, 6 patients). Clinical and radiological parameters were assessed by a postoperative comparison between the 2 groups. Results: phimain pancreatic duct after operation was dilated in all 11 patients in the non-dilated group, and the difference was significant (p=0.0003, mean dilatation ratio = 2.6) when compared with phimain pancreatic duct before operation. In contrast, the mean phimain pancreatic duct decreased after operation (mean dilatation ratio = 0.9) in the dilated group. Clinical symptoms (5 patients), impaired endocrine and exocrine pancreatic function (4 and 3 patients, respectively), elevated serum amylase level (6 patients), and pancreatic parenchymal changes on radiological examinations (5 patients) were observed only in the non-dilated group. Conclusions: Degree of dilatation of main pancreatic duct seems to correspond to likelihood of anastomotic stenosis of pancreaticogastrostomy. Pancreaticogastrostomy has less reliability in terms of the long-term patency in cases having non-dilated main pancreatic duct.