BACKGROUND AND AIMS: To determine the usefulness of the extracorporeal shock wave lithotripsy (ESWL), we analyzed mean number of shock waves, mean number of sessions and the factors affecting the clearance rate of the ESWL in 23 patients with extrahepatic bile duct stones. We believe that this is the first report for extrahepatic bile duct stone destruction by the ESWL treatment using the piezoelectrically generated lithotriptor in Korea. METHODS: Between January 1994 and August 1997, the ESWL has been performed for 23 patients with endoscopically non-extractable stones. Before treatment with the lithotriptor, the stones were identified by combination of ultrasound and C-arm methods and shock waves were produced by a piezoelectric acoustic generator. RESULTS: The ESWL was performed successfully in 20 out of 23 patients. The clearance rate of stones was 86.9%. The clearance rate of stones and mean number of shock waves in patients with solitary stone were 87.5% (14/16) and 3,471 shock-waves, respectively. The clearance rate of stones and mean number of shock waves in patients with multiple stones were 85.7% (6/7) and 3,424 shock-waves, respectively. The clearance rate of stones and mean number of shock waves in patients with smaller than 20 mm sized stones were 87.5% (14/16) and 3,557 shock-waves, respectively. The clearanee rate of stones and mean number of shock waves in patients with bigger than 20 mm sized stanes were 85.7% (6/7) and 3,227 shock-waves, respectively. AI1 of the 3 failed lithotrypsies developed just before tranducer exchange. CONCLUSIONS: These results show that piezoelectric lithotripsy is very useful for treatment of extrahapatic bile duct stones, and that the effect in the clearance of stones is not related with the number and size of the stones. We suggest that the time of transducer exchange is closely related with the clearance rate of stones. We could clear the stones effectively by piezoelectrically generated lithotriptor with a mean number of 5 sessions and 3,500 shock waves per session.