The impact of intraoperative ultrasonography (IUS) on surgery for cystic lesions of the pancreas (CLPs) has not been fully clarified. Twenty patients with CLPs, including 5 pseudocysts and 15 true cysts, were scanned intraoperatively to evaluate the utility and practicality of IUS for CLPs. In four of the five patients with pseudocysts and two with retention cysts, the operative procedures were performed under IUS guidance. In one with a pseudocyst, IUS showed that the cyst did not involve the pancreas, and subsequently cystectomy without pancreatic resection was necessary. In one of the two patients with mucin-producing cystadenocarcinomas, IUS demonstrated a skip lesion in the duct of the pancreatic tail, which contributed to changing the operative procedure from pancreatoduodenectomy to total pancreatectomy; in the other, IUS showed that the lesion was localized in the body of the pancreas, and subsequently segmental pancreatectomy was carried out instead of scheduled pancreatoduodenectomy or distal pancreatectomy. Thus in these three patients the operative procedures were changed in light of the IUS findings. In the remaining 11, although IUS visualized CLPs clearly, it added no new information relevant to the operations. We conclude that IUS contributes to performing surgery for certain types of CLP, such as pseudocysts with severe inflammation, retention cysts with nonpalpable or invisible small cysts, mucin-producing cystadenocarcinomas, and possibly other lesions.