Mitral annular calcification (MAC) by computed tomography (CT) is reported as an independent predictor of poor outcomes. However, it currently remains unclear if quantitative MAC parameters provide more value for mitral valve disease (MVD) management, therefore, we examined the prognostic value of MAC-scores using non-contrast cardiac-CT in MVD-patients. Between January 2020 and December 2021, we prospectively enrolled 300 consecutive patients with MVD (MAC-present=80 and MAC-absent=220) undergoing preoperative cardiac-CT and mitral valve (MV) surgery. Non-contrast cardiac-CT images were used to qualitatively detect MAC (present or absent) and evaluate MAC-scores. For analyses, we also collected baseline clinical data, intra-operative conversion (from MV repair to MV replacement) and follow-up arrhythmia data. Compared with the MAC-absent group, MAC-present patients were older (62±7vs.58±9 years, p<0.001), mostly women (55%vs.39.5%, p=0.017), and also had aortic valve calcification (57.5%vs.23.2%, p<0.001), mitral stenosis (82.5%vs.61.8%, p<0.001), atrial fibrillation (AF, 30%vs.11.8%, p<0.001), and larger left atrial end-diastolic dimension [LADD, 49(44-56)vs.46(41-50), p=0.001]. Furthermore, MAC-present patients underwent more MV replacements (61.8%vs.82.5%, p=0.001) and experienced a higher intra-operative conversion prevalence (11.8%vs.61.3%, p<0.001). Multiple logistic regression analyses showed that the female gender [odds ratio (OR)/95%confidence interval (CI)/p=2.001/1.042-3.841/0.037] and MAC-scores (OR/95%CI/p=10.153/4.434-23.253/p<0.001) were independent predictors of intra-operative conversion. During a follow-up of 263±134 days, MAC-present patients had more arrhythmias (42.5%vs.9.5%, p<0.001). Also, MAC-scores [hazard ratio (HR)/95%CI/p=6.841/3.322-14.089/p<0.001] and LADD (HR/95%CI/p=1.039/1.018-1.060/p<0.001) were independently associated with arrhythmias by Cox regression analyses. Non-contrast cardiac CT-derived MAC-scores showed high risk for intraoperative conversion and follow-up arrhythmias in MVD-patients. This article is protected by copyright. All rights reserved.