A system for precision guidance of surgical procedures on a patient, comprising: a) a three-dimensional digital representation of the pre-procedural geometry of a part of the patient, b) a three-dimensional digital representation of the post-procedural geometry of the part of the patient, c) a movable electro-optical camera configured to be mounted in a known position and orientation relative to a surgeon such as a head mount, d) a first carrier comprising at least 3 targets to be observed by the camera, said carrier configured to be mounted in a known position and orientation relative to a part of the patient, e) a second carrier comprising at least 3 targets to be observed by the camera, said carrier mounted in a known position and orientation relative to an element outside of the patient, f) a computer for calculating the relative positions of the first and second carriers (5, 7) with at least 3 targets, and of the camera, based on observations from the camera, g) a display, the computer and the display configured to display the projection of the three-dimensional representation of the pre-procedural or the post-procedural geometry of the part of the patient calculated by a software residing on the computer in order for the displayed projection to match with the surgeon's current physical view of the part of the patient, characterized in that h) the part of the patient as defined in feature d) is the part of the patient as defined in features a) and b), i) the second carrier is mounted in a known position and orientation relative to an implant or other structure to be attached to the part of the patient, and j) the computer and the display are configured to show how the implant or other structure to be attached to the part of the patient should be moved relative to the part of the patient to reach the desired position. a) a three-dimensional digital representation of the pre-procedural geometry of a part of the patient, b) a three-dimensional digital representation of the post-procedural geometry of the part of the patient, c) a movable electro-optical camera configured to be mounted in a known position and orientation relative to a surgeon such as a head mount, d) a first carrier comprising at least 3 targets to be observed by the camera, said carrier configured to be mounted in a known position and orientation relative to a part of the patient, e) a second carrier comprising at least 3 targets to be observed by the camera, said carrier mounted in a known position and orientation relative to an element outside of the patient, f) a computer for calculating the relative positions of the first and second carriers (5, 7) with at least 3 targets, and of the camera, based on observations from the camera, g) a display, the computer and the display configured to display the projection of the three-dimensional representation of the pre-procedural or the post-procedural geometry of the part of the patient calculated by a software residing on the computer in order for the displayed projection to match with the surgeon's current physical view of the part of the patient, h) the part of the patient as defined in feature d) is the part of the patient as defined in features a) and b), i) the second carrier is mounted in a known position and orientation relative to an implant or other structure to be attached to the part of the patient, and j) the computer and the display are configured to show how the implant or other structure to be attached to the part of the patient should be moved relative to the part of the patient to reach the desired position.