From May 1992 to October 1993, 150 ureteral stones, impervious to piezoelectric extracorporeal shock wave lithotripsy (ESWL) with ultrasound localization (EDAP LT.01), were treated with the Lithoclast. The maximum dimensions varied from 5 to 25 mm with a mean of 11 mm. 46 calculi were situated in the pelvic ureter, 82 in the abdominal ureter, and 22 were stuck in the ureteropelvic junction. There was no complete failure of fragmentation, but 39 abdominal calculi (48%) required additional treatment by ESWL due to migration of the fragments into the calyces. Apart from a few needle-sized perforations, ureteral tissue was not damaged by the Lithoclast. The use of this endoscopic lithotripter, which is highly efficient and painless, is, however, limited by the significant effect of retrograde propulsion of very mobile stones or fragments in the urinary tract.