Abstract: A surgical method and apparatus for accurately aligning the trajectory of, guiding of, and introducing or withdrawal of an instrument is disclosed. The apparatus includes a base which has a movable member movably attached to the base. The movable member has a passage therein which forms a portion of the trajectory path. A positioning stem further includes a first locator and a second locator. The first and second locators are associated with two different portions of the positioning stem so that they are essentially two points on a line. The first and second locators are also locatable by a scanning or imaging system. The positioning stem is removably attached to said movable member and used to position the movable member. Moving the movable member also moves the passage therein to different trajectories. Once the passage within the movable member more or less is aligned with a target within the body, a locking member locks the movable member into a fixed position.