We compared in a prospective study including 82 patients treated with ORIF of an intraarticular calcaneus fracture the quality of fluoroscopy, intraoperatively Iso-C(3D) and postoperative CT-scans. Therefore the posterior facet of the calcaneus (PFOC) was divided into three sectors. Joint steps and fracture gaps were detected by two independent investigators and statistically analysed. Another focus was to evaluate if the findings due to intraoperatively Iso-C(3D) assessment performed by the surgeon were correct and subsequently influenced the surgical procedure. There were no statistically differences between the Iso-C(3D)- and CT findings concerning joint steps or fracture gaps in PFOC sectors I-III. With fluoroscopy an assessment of the PFOC sectors I and II was not possible. In six cases (7.3%), intraoperative reduction was redone after performing an Iso-C(3D) scan. In ten cases, 12 malpositioned screws were replaced (12.2%/14.6%). These results suggest that intraoperative 3D Iso-C(3D) imaging provides a high diagnostic reliability. By careful assessment of the images the surgeons receive information which could lead to a change of the operative strategy.