Aims: Immature articular cartilage has a different celularity from mature articular cartilage. Thus, the healing response may be different between these tissues. In this study, we investigated the role of IGF-I in full-thickness articular cartilage defects between immature and mature rabbits. Methods: This study used 36 immature and 36 mature New Zealand rabbits. Full-thickness articular cartilage defects in the medial femoral condyle were created. Spontaneous evolution occurred in 36 animals (18 immature and 18 mature). The other 36 animals were treated with a locally administrated IGF-I. The animals were killed in groups of eight at 4th, 8th and 12th weeks. Macroscopic, histopathologic and biochemical results were evaluated and analyzed statistically. Results: Serum IGF-I levels were signiþcantly higher in the immature group than the mature group (p< 0.001). Serum IGFBP-3 levels were signiþcantly higher in the mature group than the immature group (p< 0.05). Immunuhistochemical investigation showed chondrcyte proliferation in both groups, but duration of cell proliferation and healing process were shorter in the immature groups. The cell morphology was different between the groups. Local IGF-I treated groups had better histological scores than the control groups at all weeks (p< 0.001). Conclusions: The healing response in mature and immature cartilage were similar but the duration of this healing process was shorter in the immature group and repairing cell morphology was similar to that of the normal chondrocyte.