Thirty-four glutaraldehyde-preserved porcine aortic valves have been implanted in children at the Center of Thoracic and Cardiovascular Surgery in Göttingen since 1972. Severe stenosis of the right ventricular outflow tract (RVOT) due to massive calcification of the bioprosthetic valve was detected 15 to 76 months after surgery in 2 of 3 children with hospital-made, and in one of 25 children with commercially available valved conduits. The results with Hancock xenograft valves in mitral position were even more alarming. Five out of 6 children, aged 5 to 15 years (mean 9 years) presented similar massive calcification patterns of the bioprosthesis, necessitating reoperation from 23 to 63 months (mean 38.8 months) after implantation. Focal calcium deposits were found mostly in the central layers of the cusps; severe stenosis and regurgitation were due to immobilization of the leaf-lets which were fixed in a semi-open position. The causes for early valve dysfunction and calcification of glutaraldehyde-fixed porcine aortic bioprostheses in children remain to be further investigated. Degenerative changes have been shown to commence early after implantation, resulting in collagen disruption as early as 2 years later (3, 7, 19). There is evidence that these lesions could be predisposing factors for calcification, leading to accelerated calcification rats in children and patients with a high-calcium-turnover. The use of bioprostheses in children and adolescents must therefore be questioned since they appear to carry a high prospect to early valve deterioration.