BACKGROUND Despite the fact that early and midterm hemodynamic and clinical results of the Cryolife O'Brien (CLOB) stentless valve have been reported to be favorable, the long-term durability and clinical results of this valve are largely unknown. Accordingly, we analyzed 10-year outcomes after aortic valve replacement with this valve. RESULTS From January 1994 to September 2004, 185 patients (67, 73, and 75 years, 25th, 50th, and 75th quartiles, respectively; 38% older than 75 years; 56% females) underwent aortic valve replacement with the CLOB valve. Sixty-eight percent of patients were in NYHA class 3 to 4. Standard EuroSCORE was 7.1+/-2.7. Pure aortic stenosis accounted for 42% (n=79), and pure insufficiency for 12% of cases (n=22). Concomitant surgery: 28% coronary artery bypass (n=51), 11% mitral valve replacement/annuloplasty (n=21), and 2% ascending aorta replacement (n=3). Sixty-one percent of patients received a 23-mm valve or smaller size. Follow-up was 100% completed, and cumulative follow-up was 65 months/patient. The 30-day mortality was 5.4% (none were valve related). Actuarial survival at 5 and 10 years were 68% and 40%, respectively. Actuarial freedom from structural valve deterioration was 91% at 5 years and dropped to 44% at 10 years. Actuarial freedom from reoperation was 94% at 5 years and declined to 57% at 10 years. CONCLUSIONS In a population with a high prevalence of elderly females with small aortic root, the CLOB valve demonstrated satisfactory clinical results till 8-years. Afterward, a significant increase in hazard for structural valve deterioration and reoperation occurred in late follow-up.