Purpose: To evaluate the accuracy of a newly developed open-source system for three-dimensional dental implant planning and fully guided dental implant placement. Materials and Methods: Forty-eight implant positions were planned for eight partially edentulous anatomical patient equivalent models with an opensource implant planning system on the basis of cone beam computed tomography (CBCT) scans. The virtual software planning leads to an output of four different coordinates for each implant position; with these, surgical guides were manufactured using a coordinate-transfer apparatus. During the surgical simulation, drills and implants were fully guided as they were inserted by means of the harmonized components of the vendor's sleeve-in-sleeve system. After follow-up CBCT investigation and reference marker-based software registration, linear horizontal, vertical, and maximal 3D deviations, as well as angular deviations, between the virtual planning data and the surgical results were calculated. Results: The mean three-dimensional deviation values for the final implant positions were 671 µm (95% confidence interval [CI] 452 to 891 µm) at the implant base and 808 µm (95% CI 646 to 971 µm) at the implant tip. Mean vertical deviations were 273 µm (95% CI 200 to 345 µm). Mean angular deviations of 1.9 degrees (95% CI 1.4 to 2.4 degrees) were measured. Conclusions: The open-source implant planning system described in this study demonstrated a level of accuracy that is equal or superior to most descriptions of the literature on computer-aided implant dentistry, allows for predictable implant positioning, and has the potential to reduce postoperative impairment versus conventional implant insertion. Schlagwörter: computer-aided implant placement, computer-aided surgery, cone beam computed tomography, implant dentistry, surgical templates