This study evaluated national trends, clinical outcomes, and cost implications of mitral valve (MV) repair, versus replacement, concomitant with aortic valve replacement (AVR).Patients who underwent MV surgery concomitant with AVR, between 1999 and 2008, were identified in the Nationwide Inpatient Sample (NIS) registry. Mitral stenosis, endocarditis, and emergency cases were excluded. Inpatient clinical outcomes and costs were compared. Costs were derived using cost-to-charge ratios supplied by the dataset for each individual hospital. Multivariable logistic and linear regression analyses were used for risk adjustment.A total of 41,417 concomitant cases were identified, of which 11,472 (28%) were MV repairs. Repair rates increased from 15.3% in 1999 to 43.5% in 2008 (P < .001). Major postoperative morbidity rates were similar with MV repair, versus replacement, concomitant with AVR (each 29%, P = .54). Unadjusted inpatient mortality (7.9% vs 10.1%, P = .005); length of hospital stay (median: 8 vs 9 days, P < .001); and costs (median: $45,455 vs $49,648, P < .001) were lower with MV repair. After risk adjustment, MV repair was associated with lower odds of inpatient mortality, and with lower costs (each P < .001).Mitral valve repair concomitant with AVR is associated with reduced inpatient mortality and costs, compared with MV replacement, supporting its use when technically feasible. Although use has increased substantially, MV repair continues to comprise a minority of concomitant AVR cases, in centers reporting to the NIS registry. Increasing repair rates, particularly in NIS-participating hospitals, seems prudent.