Introduction. We report a single-centre, prospective, randomised study for pedicle screw insertion, by using a Computer Assisted Surgery (CAS) technique with three dimension (3D) intra-operative images intensifier versus conventional surgical procedure. Methods. 143 patients (68 women and 75 men) were included in this study. 72 patients underwent conventional surgery (C = conventional). 71 patients were operated on with the help of a 3D intra-operative imaging system (N = navigated). We performed 34 percutaneous surgeries in group N and 37 in group C; 25 open surgeries in group N and 35 in group C. 382 screws were implanted in group C and 174 in group N. We measured the pedicle screw running-time, and surgeon's radiation exposure. All pedicle runs were assessed according to Heary's classification by two independent radiologists on a post-operative CT. Results. 3D Fluoro-navigation appeared less accurate with percutaneous procedures (24% of misplaced pedicle screws versus 5% in Group C) (p=0,007), but more accurate in opened surgeries (5% of misplaced pedicle screws versus 17% in Group C) (p=0,025). In this study, 3D-fluoroscopy navigation increases the instrumentation time, with a strongly higher radiation rate. Conclusion. Therefore, our work hypotheses are partially confirmed according to the type of analysed criteria