The risk of operative mortality in patients undergoing a first reoperation for bioprosthetic failure was assessed in a series of patients reoperated upon during the last two decades (1970-1990). A total of 330 such patients underwent replacement of 351 bioprostheses: 88 had aortic; 221 mitral; and 21 mitral and aortic bioprosthetic replacement. Indication for reoperation was in most cases structural valve deterioration (87%), followed by periprosthetic leak (7%) and endocarditis (6%). The operative mortality was significantly higher in patients who preoperatively were in New York Heart Association Functional Class IV or had a lower left ventricular function, in those reoperated because of prosthetic infection, and in those reoperated on an emergency basis. Structural valve deterioration was associated to a substantially low risk; operative mortality has improved in recent years, regardless of the indication for reoperation, partly due to the increasing experience and improved surgical techniques. Our results indicate that in recipients of bioprosthetic valves, careful follow-up with closer surveillance of valve and cardiac function and earlier prosthetic replacement might contribute to reducing the risk of reoperation.