Twenty-two patients with calculi in their horseshoe kidneys were primarily treated with extracorporeal shock wave lithotripsy on the Siemans Lithostar Plus to define the role this technique as monotherapy in horseshoe kidneys. Although a good or fair initial fragmentation was achieved in 20 of the patients (91%), repeated treatments were required in 7 (32%) of them. Fourteen patients (64%) were stone free at 3 months and an additional two had been rendered stone free at 6 months. Four patients had residual fragments no more than 0.4 cm in diameter after the treatments. The remaining two patients required secondary procedures because of inadequate fragmentation.