The goal of using navigation systems in total hip arthroplasty (THA) is to minimise malpositioned components, increase range of motion, and decrease the risk of dislocation, which may result in long-term stability. The two systems used to navigate the acetabular component are CT-based and fluoroscopy-based. Between May 2001 and May 2002, surgery was performed on 153 patients using navigation systems for cup positioning. The CT-based system was used in 46 patients and fluoroscopy-based system in 107. The diagnoses were primary osteoarthritis in 120 of the patients, and secondary osteoarthritis following congenital and post-traumatic deformities in 33. The outcomes of the operations were investigated clinically and radiologically. Mean variation of the postoperative abduction angle to the preoperative planning was 2.7 (0-8) after CT-based navigation and 3.9 (0-9) after fluoroscopy-based navigation. After the first 30 surgeries with each system, the operating time was extended by 9 minutes using the CT-based system and by 13 minutes with the fluoroscopy-based system compared to hand implantation. Also, the preoperative planning using the CT-based system was more time-consuming. No additional planning was necessary with the fluoroscopy-based system was used. Both systems were accurate and provided an improved reproducible quality. The CT-based system provided a link between the preoperative planning and intraoperative placement of acetabular components. Only a minimal difference was noted when compared to the fluoroscopy-based procedure; however, the time-consuming set up remains a problem. The advantage in using the CT-based system is the three-dimensional feed back of anatomic landmarks, but a disadvantage is the time-consuming preoperative procedure (CT-scan, data transfer, planning). For this reason the CT-based method should be performed in cases of congenital and post-traumatic deformities. The fluoroscopy-based method is easier to handle in routine cases with normal anatomy or lesser deformities. Both systems present an excellent additional tool to improve reproducible quality in THA.