This study included survey and mobility tests of subjects with hip disarticulation (HD) or hemipelvectomy (HP) before and after fitting a new prosthetic hip joint system. Physical therapy and enhanced comfort of the pelvic socket increase the acceptance of a prosthesis. The benefits of new prosthetic hip components have previously been shown in case reports only. The aim of this study was to evaluate changes in independence by use of a new prosthetic hip joint system. Thirteen HD amputees and three HP amputees were enrolled. After a baseline interview and clinical mobility tests with their existing prosthesis, the participants were fitted a new prosthesis with the Helix3D Hip and a C-Leg. The pelvic socket was made and the prosthesis was aligned according to the instructions of the manufacturer. After a mean (SD) acclimation period of 11 (6) weeks, the subjects underwent the same interview and tests. Significant improvements by use of the new prosthesis were demonstrated for the Locomotor Capabilities Index-5 (p = 0.003) and a score for activities explicitly difficult for these amputees (p = 0.008). Specific functional assessments were significantly improved with the new prosthesis. The time required for walking down a defined ramp and staircase was also significantly reduced with the new prosthesis. The new prosthetic hip joint system improved the mobility and independence of subjects with HD and HP. Prosthesis rejection is a common phenomenon after HD and HP. Main reasons are low walking speed and dependence on walking aids. The present study was able to demonstrate that the appropriate selection of prosthetic components may result in significant improvements in mobility and independence of these amputees.