Objective: This study was an investigation of the experience of a single institution with cases of definitive or suspected Mirizzi syndrome (MS) based on endoscopic retrograde cholangiography (ERCP) findings and the correlation of the preliminary diagnosis to the final diagnosis. Materials and Methods: This retrospective study was performed with the data of 58 patients treated between January 2010 and December 2019. Cases where the gallbladder or cystic duct compression of the main hepatic duct was clearly visible as the cause of biliary obstruction were classified in the ERCP report as definitive MS, and those with only a suspicion of compression were reported as suspected MS. In all, 22 patients had a definitive diagnosis of MS and 36 patients had a report of suspected MS. The ERCP reports were compared with surgical reports and the results were analyzed. Results: Examination of the surgical reports of the 22 patients with a preliminary diagnosis of definitive MS based on the ERCP findings revealed that MS was confirmed in 15 patients (68%) and malignancy in 3 patients (14%). No pathology other than gallstones was detected in 4 patients (18%). Review of the surgical reports of the 36 patients with a preliminary diagnosis of suspected MS indicated that MS was detected in 5 patients (14%), malignant stenosis in 20 patients (55%), chronic pancreatitis in 1 patient (3%), and a choledochal cyst in 1 patient (3%). Of the 23 patients with malignancy, cholangiocarcinoma was detected in 16 patients, pancreatic cancer in 3 patients, and gallbladder cancer in 3 patients. Conclusion: The results of this study illustrate the difficulty in accurately diagnosing MS and the frequent confusion with malignancy.