Abstract Background. Although numerous reports have documented declining mortality rates associated with coronary artery bypass surgery in recent years, it is unknown whether similar trends have occurred with valve surgery during this time. Methods. We conducted a regional, prospective study to assess trends in patient casemix and in-hospital mortality rates over time with aortic valve replacement (AVR), mitral valve replacement (MVR), and mitral valve repair. Data were collected from all patients undergoing AVR (n = 2,596), MVR (n = 759), or mitral valve repair (n = 522) in Northern New England between January 1992 and December 1997. Logistic regression was used to identify significant predictors of in-hospital mortality and to calculate risk-adjusted mortality rates. Results. For AVR, the trend in patient casemix was toward increased risk with increases in patient age and in the proportion of patients with: body surface area less than 1.7, diabetes, coronary artery disease, and prior valve surgery. A decrease was noted in the proportion of patients undergoing additional surgical procedures. For MVR, patient risk improved over the time period with fewer female patients and fewer patients with coronary artery disease. For mitral valve repair patient risk increased over the time period with increases in the proportion of patients with coronary artery disease, diabetes, and whose surgical priority was classified as urgent. In addition, there was a borderline significant increase in the proportion of mitral valve repair patients in New York Heart Association class IV preoperatively. Risk-adjusted mortality decreased 44% from 9.3% in 1992 through 1993 to 5.3% in 1996 through 1997 for patients undergoing AVR ( p = 0.01) and decreased 53% from 13.6% in 1992 through 1993 to 8.2% in 1996 through 1997 for patients undergoing MVR ( p = 0.01). We observed a statistically insignificant increase in risk-adjusted mortality over the time period for patients undergoing mitral valve repair (from 3.6% in 1992 through 1993 to 5.0% in 1996 through 1997; p = 0.34). Conclusions. Significant improvement in mortality rates with valve replacement was observed in northern New England during this time period. This improvement persisted following adjustment for changes in patient casemix over this time. These trends mirror improvements in mortality with other cardiac surgical interventions that have been observed in recent years in our region and nationally.