The treatment results obtained in children using an unmodified Dornier HM3 or a Medstone STS lithotripter for renal and ureteral stones were compared. The Dornier HM3 was used to treat 28 renal and 10 ureteral stones, while the Medstone STS was used to treat 73 renal and 34 ureteral stones. The treatment results were compared using the chi-square test to determine statistical significance. The stone-free rate, retreatment rate, and post-SWL secondary-procedure rate were 68%, 4%, and 0, respectively, with the Dornier HM3 and 93%, 6%, and 3.6%, respectively, with the Medstone STS for single renal stones and 80%, 0, and 0, respectively, with the Dornier HM3 and 82%, 0, and 5.9%, respectively, with the Medstone STS for single ureteral stones. Abnormal anatomy (horseshoe kidney, allograft kidney) or functional interference with the passage of fragments (urinary diversion, neurogenic bladder) was present in 16% of the children treated with the Dornier HM3 compared with 5% of those treated with the Medstone STS (p = 0.36). The treatment results with the unmodified Dornier HM3 and the Medstone STS were similar except for the statistically significantly higher stone-free rate for single renal stones obtained with the Medstone STS. The difference was most likely attributable to the smaller number of children with abnormal anatomy or functional interference with the passage of fragments who were treated with the Medstone.