Clinical results of distraction osteogenesis with transplantation of marrow-derived mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP) were reviewed in three femora and two tibiae of the two patients with achondroplasia and one patient with congenital pseudarthrosis of the tibia. MSCs derived from the iliac crest were cultured with osteogenic supplements and differentiated into osteoblast-like cells. PRP, which is known to contain several growth factors and coagulate immediately by a minute introduction of thrombin and calcium, was prepared just before transplantation. Culture-expanded osteoblast-like cells and autologous PRP were injected into the distracted callus with the thrombin-calcium mixture so that the PRP gel might develop within the injected site. Transplantation of MSCs and PRP was done at the lengthening and consolidation period in each patient. The target lengths were obtained in every leg without major complications and the average healing index was 23.0 days/cm (18.8-26.9 days/cm). Although these results are still preliminary, transplantation of osteoblast-like cells and PRP, which seemed to be a safe and minimally invasive cell therapy, could shorten the treatment period by acceleration of bone regeneration during distraction osteogenesis.