A 59-year-old woman was referred for investigation of a pancreatic cystic lesion. Computed tomography revealed a well-demarcated, multilocular cyst, approximately 4 cm in size, at the pancreas head. Endoscopic ultrasonography demonstrated honeycomb-like components at the cyst margin. The cyst was associated with a widely-dilated upstream main pancreatic duct (MPD). Endoscopic retrograde pancreatography demonstrated a communication between the stenotic Santorini‘s duct and the cyst. Aspiration cytology from the cyst demonstrated clusters of mucinous epithelial neoplasm cells. Branch-type intraductal papillary mucinous neoplasm, possibly invading to the MPD, was suspected and pancreatoduodenectomy was performed. Surprisingly, pathology of the resected pancreas showed mixed-type serous cystadenoma.