The advantages of endoscopic transethmosphenoidal surgery for pituitary tumors using a navigation system were reported. The surgical technique was as follows. First, sphenoidal sinuses were opened via the bilateral ethmoidal sinuses and the olfactory clefts. Then the septum of the sphenoidal sinuses was resected. Next, an endoscope was inserted via the left nasal cavity and fixed in place. The tumor was then removed via the right nasal cavity. Our approach for pituitary tumors provided sufficient working space and permitted the surgeon to carry out the procedure using both hands. In addition, use of the InstaTrak System made it possible to recognize the orientation of the surgical field in the sella turcica. Thus, the tumor could be resected more easily and safely. It is concluded that this approach will be particularly useful for patients with narrow nasal cavities or poor development of the paranasal sinuses.