Autologous chondrocyte transplantation (ACT) is a newly therapy option for treatment of cartilage damage. Since 1996 we performed the ACT in 10 patients with 14 cartilage damages. Magnetic resonance imaging (MRI) is a non-invasive method for postoperative controlling the transplantation area. The MRI showed in the first 3-6 months postoperatively signal irregularities with partial gadolinium uptake at the transplantation site. Arthroscopically the transplantation site was spongy, when it was probed and at the histological examination there was a hyalinlike appearance of the cells. 1 year postoperatively it seemed that process of reparation was finished. There was no more Gadolinium-uptake at the transplantation site and the borders of the transplant were hardly visible. The histological examination revealed hyalinlike repair tissue with a more columnar appearance of the cells. The Lysholm Score improved from 78 to 92 points, 1 year postoperatively.