The ROBODOC system was designed to address potential human errors in performing cementless total hip replacement. The system consists of a preoperative planning computer workstation (called ORTHODOC) and a five-axis robotic arm with a high speed milling device as an end effector. The combined experience of the United States Food and Drug Administration multicenter trial and the German postmarket use of the system are reported. The United States study is controlled and randomized with 136 hip replacements performed at three centers (65 ROBODOC and 62 control). Followup was 1 year on 127 hip replacements and 2 years on 93 hip replacements. No differences were found in the Harris hip scores or the Short Form Health Survey outcomes questionnaire. Length of stay also was not different, but the surgical time and blood loss were greater in the ROBODOC group. This was attributed to a learning curve at each center. Radiographs were evaluated by an independent bone radiologist and showed statistically better fit and positioning of the femoral component in the ROBODOC group. Complications were not different, except for three cases of intraoperative femoral fracture in the control group and none in the ROBODOC group. The German study reports on 858 patients, 42 with bilateral hip replacements and this includes 30 revision cases for a total of 900 hip replacements. The Harris hip score rose from 43.7 to 91.5. In these cases the surgical time declined quickly from 240 minutes for the first case to 90 minutes. No intraoperative femoral fractures occurred in 900 cases. Other complications were comparable with total hip replacements performed using conventional techniques. The ROBODOC system is thought to be safe and effective in producing radiographically superior implant fit and positioning while eliminating femoral fractures.