The majority of cystic lesions of the pancreas are psudocysts and a small fraction neoplastic. Failure to recognize the true nature of neoplastic cyst will lead to an incorrct treatment strategy. Ultrasonography, computerized tomography and angiography were used to distingish these lesions, but diagnostic value of ERCP is in controversy. To evaluate the diagnostic value of ERCP in cystic lesions of the pancreas, we analysed 33 cases of pancreatic cystic lesions (pseudocyst 18 cases, retention cyst 3 cases and cystic, neoplasm l2 cases) between Apr. 1985 and June 1993. In 18 cases of pseudocysts, ERP findings were communication with cyst in 8 cases (44.4%), chronic pancreatitis in 8 cases (44.4%), obstruction in 4 cases (22.2%) and displscement of pancreatic duct in 2 cases (11.1%), and ERC findings, which were perfomed in 8 cases, showed cholangitis in 3 cases (37.5%), CBD stone in 2 cases (25%), mass effect in 1 case (12.5%) and normal in 2 cases (25%). There was no communication with the cyst and pancreatic duct, except two mucinous ductal ectasia, in 12 cases of cystic neoplasms, and the other findings were displacement of pancreatic duct in 4 cases (33.3%), obstruction in 2 cases (16.7%) and normal in 4 cases (33.3%). ERC findings of cystic neoplasm were almost normal (85.7%) except 1 case of cholangitis. In conclusion, ERCP findings of pseudocysts were communication with pancreatic duct, chronic pancreatitis and biliary tract abnormality. In contrast, ERCP findings of cystic neoplasms were displacement or obstruction of pancreatic duct without communication and chronic pancreatitis, and biliary tract abnormality were rare.