The Siemens Lithostar lithotriptor was used to treat 20 children (4 to 17 years old) with renal or ureteral calculi. Two patients had bilateral renal and 2 had ureteral calculi. Of 34 calculi treated 47% were in the renal pelvis, 29% in the lower calix, 12% in the upper calix, 3% in the middle calix and 9% in the upper ureter. Stone size ranged from 2 X 2 to 40 X 20 mm. and averaged 10 X 7 mm. Of the children 60% were treated while they were under neuroleptic anesthesia. No major complications were encountered. The 3-month rate free of stones after 1 treatment was 60% and increased to 80% with multiple treatments. The success rate, defined as being either free of stones or with residual fragments equal to or less than 4 mm. in diameter, was 95%. We conclude that lithotripsy with the Lithostar device in children, at least for the short term, is safe and effective.