The percutaneous nephrolithotomy is a minimally invasive surgery that is employed to remove larger stones (calculi) in the kidney. This technique places a nephroscope into the kidney through a small tract set after a small incision in the patients back. During the tract positioning, there are risks of kidney bleeding and of injury of other organs near the kidney such as the bowels, spleen or lever. In order to minimize this risks a preoperative planning helps for the choice of the best kidney calyx target and for the definition of the optimal track to reach this target. Our study is focused on the development of a computer tool that will help establishing the preoperative planning on patient specific data. Especially, this tool allows defining interactively and visually the optimal track on a 3D volume data acquired on the patient, simulating the effect on the anatomy of the real passageway and finally gives the necessary information back to the surgeon in order to transpose during the intervention the defined optimal track