BACKGROUND AND PURPOSE: Shockwave lithotripsy (SWL) has become a first-line intervention for treatment of nephrolithiasis. However, few studies have examined the effects of modifications in the method of shockwave energy administration on comminution efficiency. We propose that a gradual increase in output voltage will produce superior stone fragmentation in comparison with a constant or a decreasing output voltage by optimizing the stress wave and cavitation erosion forces on renal calculi. MATERIALS AND METHODS: BegoStone phantoms were implanted in the renal pelvis of 11 pigs that underwent SWL at a pulse repetition rate of 1 Hz. Animals in the increasing strategy group (N = 4) were subjected to 18, 20, and 22 kV for 600, 600, and 800 shocks, respectively. The second group (N = 4) received a decreasing strategy of 22, 20, and 18 kV for 800, 600, and 600 shocks, respectively. The third group (N = 3) received all 2000 shocks at 20 kV, mimicking the clinical protocol. RESULTS: A progressively decreasing strategy and constant output voltage produced a mean comminution efficiency, or percentage of stone fragments <2 mm, of 89.0% +/- 3.3% and 87.6% +/- 1.7%, respectively. The mean comminution efficiency was improved to 96.5% +/- 1.4% by using the increasing strategy (P = 0.01). CONCLUSIONS: A progressive increase in lithotripter output voltage during SWL can produce greater stone fragmentation than protocols employing constant or decreasing output voltage.