Background and aim of the study: The Hancock II bioprosthesis (HII) has several design features designed to increase its durability. The study aim was to determine very long-term outcomes for the HII valve in a large patient population. Methods: Long-term follow up was obtained by mail and/or telephone questionnaire of patients undergoing HII valve replacement surgery between 1982 and 2001 (n = 1,569). Follow up was complete on 1,568 patients (99.9%), and ranged from 0 to 250 months. Results: Isolated aortic valve replacement (AVR) was performed in 1,010 patients and mitral valve replacement (MVR) in 559. The average (+/- SD) age of patients was 67 +/- 11 years, and 65% were males. Long-term death occurred in 445 AVR patients and 275 MVR patients, of which 11% and 17%, respectively, were valve-related. Twenty-year freedom from thromboembolism (all results actuarial) was 79 +/- 3% after AVR and 83 3% after MVR; freedom from endocarditis was 91 +/- 5% and 85 5%, respectively. Twenty-year freedom from structural valve deterioration (SVD) was 73 +/- 16% and 39 +/- 9% in AVR patients aged :65 years and <65 years, respectively. Similarly, 20-year freedom from SVD was 59 11% and 27 9% in MVR patients aged 65 years and <65 years, respectively. When actual statistical techniques were applied (cumulative incidence), 20-year actual risk of SVD was 18 +/- 3% in all AVR patients and 23 +/- 3% in all MVR patients. Reoperation was required in 72 AVR patients, and was valve-related in 60. A total of 49 MVR patients underwent reoperation; 48 of these were valve-related. Conclusion: The Hancock II bioprosthesis continues to show very good long-term results and durability, particularly in patients aged over 65 years.