Steward et al. (2005) reported successful granulocyte colony-stimulating factor (G-CSF)-based HSC mobilization in two patients with atypical osteopetrosis, having a poor CD34+ cell count in peripheral blood, to guarantee an adequate autologous backup before transplantation. However, there are no other reports of hematopoietic stem cell (HSC) mobilization in children with classical severe ARO so far. If proven safe and effective, this approach could favor the harvest of an adequate amount of CD34+ cells from the blood for autologous back-up transplantation (Box 1) or gene correction. Here, CD34 is linked to osteopetrosis.