OBJECTIVE: Few studies have reported on aortic valve replacement (AVR) in patients aged >80 years who have small aortic annuli. Various surgical techniques have been proposed for treating such patients. We investigated AVR using small-diameter mechanical valves, in patients aged >80 years, to determine its effectiveness. METHODS: Eighteen consecutive patients (15 women; 3 men) aged >80 (mean: 83.3 ± 2.7) years underwent surgical AVR with a 17-mm prosthesis. The clinical status and results of pre- and post-operative echocardiography were evaluated. Midterm examination was conducted at 12.0 ± 1.0 months after AVR. RESULTS: The average preoperative body surface area of the patients was 1.39 ± 0.15 m(2); the average New York Heart Association functional class was 3.28 ± 0.75. Echocardiography showed a peak pressure gradient of 99.1 ± 38.4 mm Hg. Operative mortality was absent. A significant decrease in the peak pressure gradient was found on early (22.6 ± 7.2 mm Hg) and midterm (22.2 ± 8.0 mm Hg) postoperative echocardiography, compared with that in the preoperative period. During this follow-up, 16 patients improved to class I, a significant change in each perioperative period compared with the preoperative period. No mortality was observed at 1 year postoperatively. CONCLUSIONS: In patients aged >80 years who have small aortic annuli, AVR using a 17-mm prosthesis showed satisfactory clinical and hemodynamic results and provided a satisfactory remote prognosis.