PURPOSE: To demonstrate by CT scanning the effect of extracorporeal shock wave lithotripsy (ESWL) on pancreatic duct stones in patients with chronic pancreatitis. MATERIALS AND METHODS: Pancreatic duct stones in 11 patients with chronic pancreatitis were subject to ESWL using an electrohydraulic lithotripter. Endoscopic stone removal using a basket had failed in ten patients, and in one, endoscopy was impossible due to a previous Whipple's operation. CT scans obtained before and after ESWL were evaluated by two radiologists: the longest and shortest diameters of the target stone were measured, and according to the degree of fragmentation, determined by comparing the area of the stone before and after ESWL, a grade (1-5) was assigned. In each case, the pre- and post- treatment diameter of the main pancreatic duct, measured at the pancreatic body, was also compared. RESULTS: Disintegration of the target stone was achieved in all patients: grade 1 (over 75% of the area remained, compared with that of the initial stone) was assigned in two patients; grade 2 (51-75% of the original area) in one; grade 3 (26-50%) in four; grade 4 (under 25%) in two; and grade 5 (complete clearance of the target stone) in two. The mean area decreased from 175 mm2 to 69 mm2 after ESWL (p<0.05); a decrease of more than 50% was observed in eight patients (73%). The mean diameter of the main pancreatic duct decreased from 7.36 to 4.81 mm (p<0.05). No severe adverse effects or complications were noted, and all patients showed clinical improvement. Follow-up studies indicated that pancreatic duct stones recurred in three patients. CONCLUSION: ESWL can cause the fragmentation of pancreatic duct stones without significant complications, and should be considered where endoscopic stone removal has failed. CT is a suitable non-invasive and accurate tool for evaluating the therapeutic results of ESWL.