PURPOSE: To describe the CT and ERCP findings of mass-forming chronic pancreatitis. MATERIALS AND METHODS: CT and ERCP features were assessed in 13 patients suffering from mass-forming chronic pancreatitis. Diagnosis was on the basis of surgery (n=5), percutaneous needle biopsy (n=3), and clinical follow-up (n=5). Contrast-enhanced CT was available for all patients: five underwent dynamic study and ERCP was performed in 12. On CT and ERCP, both groups were evaluated with regard to the presence and degree of pancreatic ductal dilatation (greater or less than 50 % of total gland width), double duct sign, enhancement pattern, pancreatic parenchymal calcification (site and distribution pattern), mass identification, the direction of infiltration, pancreatic parenchymal atrophy, configuration at the site of obstruction in the pancreatic and common bile duct, lymphadenopathy, vascular encasement, and vascular engorgement or increased collateral vessels in the peripancreatic space. RESULTS: Seven of 13 patients had suffered chronic alcoholism. Serum CA19-9 levels were normal in all patients except one. Common CT and ERCP findings of mass-forming chronic pancreatitis included pancreatic duct dilatation (92.3%), double duct sign(69.2%), inhomogeneous enhancement of the mass (69.2%), and the presence of calcification (61.5%). Patterns of pancreatic duct dilation were irregular in five patients (38.4%) and smooth in three (23.1 %).In all patients, duct dilatation was less than 50 % of total gland width. Enhancement patterns of the pancreatic mass were inhomogeneous (69.2%), a nonenhancing low attenuation mass (15.3%), and homogeneous enhancement (15.3 %). Configuration at the site of obstruction in the pancreatic duct was abrupt termination in two patients (15.4 %) and smooth termination in two (15.4 %). The common bile duct teminated abruptly in three patients (23.1%), and in four (30.8 %) smooth narrowing was abserved. CONCLUSION: Common findings of mass-forming chronic pancreatitis were duct dilatation of less than 50 % of total gland width, double duct sign, inhomogeneous enhancement of the mass, and the presence of calcification. These were combined with observation of clinical findings such as chronic alcoholism and CA19-9 levels, which are useful indicators for differentiating mass-forming chronic pancreatitis from pancreatic cancer.