Mitral valve repair rather than replacement was performed in 133 of 183 patients (73%) with considerable mitral valve insufficiency requiring surgery. There were seven operative deaths (50%) and 16 late deaths in the 133 patients followed up from 1 to 15 years. Only four of the late deaths were possibly related to the underlying valvular heart disease. Repair is preferable to replacement with present-day mitral valve prostheses.