Mitral annular calcification (MAC) increases technical complexity for surgeons during mitral valve (MV) procedures. This study assesses the risks conferred by the presence of MAC in patients undergoing MV replacement (MVR) using The Society of Thoracic Surgeons Adult Cardiac Surgery Database. A total of 52,816 MVR procedures were performed between 2011 and June 2017. Individuals with concomitant tricuspid procedures were included, but those from institutions that reported < 1 MAC case/y were excluded. Operative mortality and in-hospital complications in MAC patients were compared with controls from the same institution. The contribution of hospital MV procedure volume (stratified by mean procedures per year during) to adjusted operative mortality was also assessed. Overall, 9551 MVR cases were classified as MAC (18.1%). Observed operative mortality was 5.8% for MAC and 4.4% for non-MAC patients (odds ratio [OR], 1.28; 95% confidence interval [CI], 1.19-1.38). Although postoperative stroke and reoperation rates were similar, MAC was associated with increased risk of acute kidney injury (relative risk, 1.15) and reintubation (relative risk, 1.26) (all P < .001). After risk adjustment, MAC remained a risk factor for operative mortality (OR, 1.24; 95% CI, 1.08-1.42). Centers with less than 50 MV procedures/y were also associated with increased operative mortality (OR, 1.21; 95% CI, 1.08-1.37; observed-to-expected mortality among MAC patients 1.09 vs 0.82 in centers with ≥ 50 MV procedures; P = .001) CONCLUSIONS: The presence of MAC alone, regardless of severity, was independently associated with increased operative mortality and adverse postoperative outcomes. Even after adjusting for attendant cardiovascular and metabolic comorbidities, centers with low MV case volumes were found to have worse outcomes after MVR.