To define better the performance of the bileaflet St. Jude and the tilting-disc Medtronic-Hall valves, we retrospectively analyzed 122 patients (St. Jude, 80 patients; Medtronic-Hall, 42 patients) who received simultaneous aortic and mitral replacement from May 1984 until June 1994. The two groups were not different with respect to preoperative clinical and hemodynamic parameters and New York Heart Association functional class. The hospital mortality and late mortality were not significantly different. Risk analysis identified advanced age and previous myocardial revascularization as predictors of operative death. Follow-up was complete in 96 of 103 hospital survivors (93%) and was similar in both groups. The actuarial survival, linearized rates of valve-related complications, and actuarial freedom from valve-related complications were similar in both cohorts. The presence of coronary artery disease negatively influenced the actuarial survival after simultaneous aortic and mitral valve replacement. Postoperative New York Heart Association functional class was not significantly different in either group. These data indicate that the Medtronic-Hall and St. Jude prostheses are not significantly different with respect to their clinical performance and valve-related complications for simultaneous double-valve replacement.