Abstract: The invention relates to a device for intraoperative navigation and placing of a medical implant, in particular, a prosthesis, using a mobile medical imaging device A) a position determination device (15) for the spatial position measurement of the reference elements (1) relative to a spatially-fixed coordinate system (13); B) a mobile medical imaging device (3), comprising a radiation source (10) and a receiver unit (11), C) a computer (6) connected to the position determination device (15) and comprising a screen (7) whereby D) radiation source (10) and receiver unit (11) are connected to an imaging unit (18), which may be displaced about the room in a manner as to be fixed relative to each other and E) a reference element (1) is fixed to each of the imaging device (18), the bones (2) for treatment, and the surgical instrument (14).