Annular dilation is a common feature of chronic degenerative mitral regurgitation caused by leaflet prolapse. Accordingly, patients undergoing surgical repair usually undergo concomitant reductive annuloplasty to restore a normal annular-to-leaflet relation. With the evolution of transcatheter valve repair technologies, patient selection criteria for those who do not require annuloplasty are needed. A series of patients undergoing mitral repair was analyzed, and the role of annular-to-leaflet mismatch in identifying patients requiring reductive annuloplasty was explored. Preoperative data for 82 patients undergoing mitral repair with annuloplasty for degenerative mitral regurgitation were prospectively collected, including annular intercommissural (IC) and septolateral (SL) dimensions and heights of anterior (ALH) and posterior leaflets. An SL/ALH ratio >1.4 was used to define annular-to-leaflet mismatch. After mitral repair, the ratio between preoperative IC distance and the size of the implanted annular prosthesis (Seguin ring [SR], IC/SR <1.2) was used to identify patients for whom annuloplasty was nonreductive. All patients underwent successful mitral repair. Mean preoperative IC was 46 +/- 6 mm, SL was 42 +/- 5 mm, and ALH was 31 +/- 5 mm. Mean SR was 34 +/- 3 mm, with a mean IC/SR ratio of 1.34 +/- 0.14. Sixteen patients (19%) had an IC/SR ratio <1.2. IC/SR ratio <1.2 was predicted by a SL/ALH ratio < or =1.4 (p = 0.009). In conclusion, annular dilation is negligible in <20% of surgical candidates. In this subgroup, an isolated leaflet repair may be indicated. SL/ALH ratio is a good indicator of annular-to-leaflet mismatch and could be used as an adjunct to other methods of annular function assessment to select patients for ringless mitral repair.