OBJECTIVE The study aim was to describe patterns of failure in a consecutive series of patients with the CryoLife-O'Brien stentless porcine aortic bioprosthesis. METHODS The records of patients requiring redo surgery were reviewed. All surviving patients were contacted and questioned about clinical events since implantation of the valve. RESULTS The early mortality was 7%, whilst 4% of patients died between 30 days and one year after surgery, and 31% died beyond one year. Six cases of structural deterioration were identified; five of these cases were due to a cusp tear (usually of the right coronary cusp), and one case was due to valve calcification. There were five cases of non-structural dysfunction; dehiscence was present in three of these cases, with progression of minor periprosthetic regurgitation seen immediately after surgery. Three failures occurred as a result of infective endocarditis. Structural valve deterioration or dehiscence occurred at a mean of 52 months after surgery, with no step-up in incidence at any time-point. Primary failure occurred in three of 49 (6%) bioprostheses manufactured after June 2003, and in eight of 117 (7%) manufactured before June 2003. CONCLUSIONS The incidence of primary valve failure at 52 months after implantation was found to be 7%. It is suggested that routine echocardiography be performed at least annually, particularly in those patients with even minor paraprosthetic regurgitation on the postoperative study.