Problem: Installation of fixtures for prosthetic reconstruction in the upper jaw in patients with extensive bone and soft tissue defects is still a challenge. These situations normally require the support of vascularized bone or composit grafts and secondary insertion of endosseous implants. Aims: The new fixture developed by Brånemark System achieves instant prosthetic reconstruction by anchoraging implants in the zygomatic bone to offer sufficient support even in the above described situations. The dimension of these zygomaticus fixtures and the complex anatomy due to previous surgical procedures demand specific treatment for a precise and safe insertion of the implants. Method: On the base of an axial spiral CT data set the STN-3.5 navigation system (Leibinger/Zeiss) was used for preoperative planning and intraoperative controlling of insertion of zygomaticus fixtures after subtotal maxillectomy. Bilateral insertion of zygomaticus fixtures was done substituting standard Brånemark fixtures placed in the remaining anterior maxillary bone after resection of the posterior maxilla because of a squamous cell carcinoma. Results: Computer assisted insertion of zygomatic fixtures was successfully completed. The implants could be positioned precisely as preoperatively planned. Conclusions: The use of zygomatic fixtures after ablative tumor surgery with resection of the maxillary bone provides immediate prosthetic reconstruction without additional bone grafting. Computer assisted insertion of these implants improves preoperative planning by valid 3D visualization of the anatomic situs and virtually positioning of the fixture and faciliates clinical procedure by guiding the drill to the intended position. Keywords: Rahmenlose Stereotaxie, computergestützte Chirurgie, Zygomaticus Fixture, Tumorchirurgie