peer reviewed ; Busulfan is commonly used in preparative conditioning regimens prior to haematopoietic stem cell transplantation in children and young adults for malignant and non-malignant disorders. For many years busulfan was only available in oral form, resulting in large inter- and intra-patients variability in plasma exposure, associated with higher graft failure rate as weil as higher toxicity such as veno-occlusive disease. With the development of an intravenous formulation of busulfan, a more accu rate control of both the inter- and intra-patient variability has been provided. The goal of this study was to evaluate the use and efficacy of intravenous busulfan in comparison with the oral formulation in children undergoing an autologous transplantation after conditioning with busulfan. Despite the small number of patients, this study confirmed the apparent benefit of intravenous busulfan in children undergoing an autologous HSCT. The use of a five-Ievel dose schedule defined by body weight resulted in an efficient engraftment with marked reduction in the incidence of veno-occlusive disease compared with oral busulfan. In terms of disease-free outcome, survival and event-free survival, similar results have been obtained in both groups. The choice of this formulation of busulfan should therefore be considered.