Background and study aims:Common bile duct(CBD) -compression can be caused by stones in the cystic duct(Mirizzi syndrome) which can be difficult to diagnose even with endoscopic retrograde cholangiopancreatography(ERCP) .Conventional imaging often gives insufficient information and endoscopic ultrasonography(EUS) and magnetic resonance imaging may improve diagnostic accuracy,but often the final diagnosis is made during exploratory surgery.Patients and methods:All patients undergoing ERCP during a 3-year period were prospectively analyzed if they fulfilled the inclusion criteria:gallbladder in situ;obstructive jaundice with CBD stenosis,demonstrated at endoscopic retrograde cholangiography(ERC) ,but unexplained at ultrasonography;and inability to demonstrate the cystic duct during ERC.Intraductal ultrasonography(IDUS) was carried out over a guidewire using a 20-MHz probe.Prior to ERCP,patients were evaluated with abdominal ultrasonography and computed tomography(CT) ,as well as by magnetic resonance cholan-giopancreatography(MRCP) or EUS in some.Results:74 patients out of 2089 undergoing ERCP fulfilled the entry criteria.Final diagnoses,from surgical exploration(n = 41) ,cytology(n = 21) ,or endoscopic extraction of stones from the cystic duct(n = 12) ,were Mirizzi syndrome(type I) in 30 patients and other causes in 44 patients(gallbladder carcinoma [n = 16],pancreatic carcinoma [n = 9],metastatic compression [n = 9],other [n = 10]) .CT had shown suspected Mirizzi syndrome in 1/30 cases(3%) and MRCP in 12/19 evaluated cases(63%) .EUS allowed a correct diagnosis in 11 of 15 evaluated cases(73%) .IDUS required an additional 8 ± 3 min and showed a sensitivity of 97% and specificity of 100%.Conclusion:IDUS is a sensitive and specific method for the diagnosis of Mirizzi syndrome. Background and study aims: Common bile duct (CBD) -compression can be caused by stones in the cystic duct (Mirizzi syndrome) which can be difficult to diagnose even with endoscopic retrograde cholangiopancreatography (ERCP). Conventional imaging gives promise and insufficient information and endoscopic ultrasonography (EUS) and magnetic resonance imaging may improve diagnostic accuracy, but often the final diagnosis is made during exploratory surgery. Patients and methods: All patients under exploratory ERCP during a 3-year period were prospectively analyzed if they fulfilled the inclusion criteria: gallbladder in situ ; obstructive jaundice with CBD stenosis, demonstrated at endoscopic retrograde cholangiography (ERC), but unexplained at ultrasonography; and inability to demonstrate the cystic duct during ERC. Intraductal ultrasonography (IDUS) was carried out over a guidewire using a 20-MHz probe. to ERCP, patients were evaluated with abdominal ultrasonography and computed tomography (CT), as well as by magne Tic resonance cholan-giopancreatography (MRCP) or EUS in some. Results: 74 patients out of 2089 under ERCP fulfilled the entry criteria. Final diagnoses, from surgical exploration (n = 41), cytology stones from the cystic duct (n = 12), were Mirizzi syndrome (type I) in 30 patients and other causes in 44 patients (gallbladder carcinoma [n = 16], pancreatic carcinoma [n = 9], metastatic compression [n = 9 ], other [n = 10]). CT had shown suspected Mirizzi syndrome in 1/30 cases (3%) and MRCP in 12/19 evaluated cases (63%). EUS allowed a correct diagnosis in 11 of 15 as cases 73%). IDUS required an additional 8 ± 3 min and showed a sensitivity of 97% and specificity of 100%. Conflusion: IDUS is a sensitive and specific method for the diagnosis of Mirizzi syndrome.