Introduction In recent years, there has been an increasing interest in custom triflange acetabular components (CTAC) for revision and oncological surgery. The aim of this study was to evaluate the surgical accuracy of positioning CTACs in patients receiving either total hip arthroplasty (THA) revision or tumor resection surgery, using a novel 3D analyzing technique. Method This retrospective cohort study included 35 patients (27 tumor and 8 THA revision cases), between February 2017 and March 2021. All patients received a CTAC. The planned and achieved implant position were assessed by means of a developed semi-automatic 3D-CT assessment method. The primary outcomes were the cup angles described as inclination, anteversion and cup rotation, and the translation of center of rotation (COR), pubic flange, ischial flange and ilium flange in three planes. Results The mean deviation, between planned and achieved, in inclination was 0.5° (SD: 3.9°), in anteversion 1.2° (SD: 6.1°) and in cup rotation 0.6° (SD: 3.2°). The mean deviation in COR in the sagittal plane was -0.8 mm (SD: 3.2), in the coronal plane -0.4 mm (SD: 6.3) and in the axial plane 0,6 mm (SD: 6,1). Translation of the ischial flange showed the largest aberration (median absolute value: 7.0 mm), followed by the pubic flange (6.4 mm) and the ilium flange (5.3 mm). Discussion A semi-automatic method to analyze the 3D position of CTAC was presented in this study. The results show good agreement between the planned and achieved implant position in patients receiving THA revision or tumor resection surgery. 89% of the components in this study were accurately positioned according to our criteria.