OBJECTIVE: To correlate Q3DCT measurements of residual step-off, gap, and 3D multidirectional displacement of postoperative posterior malleolar fracture fragment reduction in patients with rotational type ankle fractures, with patients' clinical outcome using standardized patient- and physician-based outcome measures. DESIGN: Prospective cohort study. SETTING: Level-I Trauma Center. PATIENTS: Thirty-one patients with ankle fractures including a posterior malleolar fracture (OTA/AO type 44) were included. INTERVENTION: All patients underwent open reduction internal fixation of their ankle fracture, of which 18 patients (58%) had direct fixation of the posterior malleolar fragment. Decision of (direct) fixation of the posterior malleolar fragment was not standardized and guided by surgeons' preference. MAIN OUTCOME MEASUREMENTS: Quality of postoperative reduction was quantified using Q3DCT: posterior fragment size (% of joint surface), residual step-off (mm), postoperative gaps (mm), and overall multidirectional displacement were quantified. Foot and Ankle Outcome Score pain and symptoms subscales and quality of life (Short Form-36) at 1 year postoperatively were included as the main outcome measures. RESULTS: Step-off (mean 0.6 mm, range 0.0-2.7, SD 0.8) showed a significant correlation with worse Foot and Ankle Outcome Score pain and symptoms subscales. Residual fracture gap (mean 12.6 mm, range 0.0-68.8, SD 19.5) and 3D multidirectional displacement (mean 0.96 mm, range 0.0-2.8, SD 0.8) showed no correlation. CONCLUSIONS: In patients with rotational type ankle fractures involving a posterior malleolar fracture, contemporary Q3DCT measurements of posterior fragment size and residual intra-articular step-off-but not gap-show significant correlation with patient-reported pain and symptoms. LEVEL OF EVIDENCE: Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.