Aim: evaluation of articular cartilage defects repair of the knee by mosaicplasty. Methods: 12 cases of 12 knees (8 males and 4 females) that underwent cartilage repair by mosaicplasty for femoral condyle defects were reviewed. Mean patient age at time of surgery was 34 years old (23 Ð 47 years). All cases were diagnosed by arthroscopy and 3 underwent preoperatively MRI. Postoperatively 5 cases were investigated by MRI, 9 underwent a second-look arthroscopy and in 2 cases we performed a needle biopsy. The average followup period from surgery was 12 months. The mean period from surgery to follow-up arthroscopy was 7 months. Results: Clinical results were appreciated by HSS Score. According to this scale the mean rate of our results was 90. All cases that underwent a second-look arthroscopy showed a good articular surface. Needle biopsy demonstrated regeneration of hyaline cartilage, even if some structural differences occurred. Conclusions: Mosaicplasty seems to be an efþcient alternative for treatment of limited cartilage defects. Needle biopsy demonstrated that regenerated hyaline cartilage in the gaps among mosaicplasty areas has not the same structure and quality like the natural cartilage. Therefore degeneration is possible and long term careful observation is needed.