BACKGROUND To determine the optimal method of repair for severe, segmental anterior leaflet prolapse, we analyzed outcome of 121 patients who underwent chordal shortening (n = 46) and chordal replacement (n = 75) from 1988 to 1996. METHODS Chordae were replaced with expanded polytetrafluoroethylene sutures. Patients had an annuloplasty with either chordal replacement or shortening. Follow-up was 100% complete (mean, 3.7 years). RESULTS Mean age was 62.1 years, 86 were men, and 60 patients had isolated valve repair. There was one hospital death and 14 late deaths for a 5-year actuarial survival of 86.4%+/-4.5%. Sixteen patients underwent reoperation, 5 in the replacement group and 11 in the shortening group. Mechanism of valve failure in the replacement group was native chordae rupture (n = 4) and neochordae dehiscence (n = 1). With chordal shortening, repair failure was attributed to rupture of shortened chordae (n = 8), leaflet prolapse with and without annuloplasty ring dehiscence (n = 2), and native chordae elongation (n = 1). Risk of reoperation because of repair failure at 3.5 years was 1.4% in the chordal replacement group and 14.8% in the chordal shortening group (p = 0.02). CONCLUSIONS Chordal replacement is superior to chordal shortening, providing a predictable method for correction of mitral regurgitation with a low incidence of reoperation.