Eight children developed osteochondroma (OS) at a mean of 88 months, after hematopoietic stem cell transplantation (HSCT). The mean age at HSCT was 56 months (12-84). This represents a cumulative incidence of 20% among patients less than 18 years of age transplanted from 1981 to 1997. These eight patients underwent allogeneic (n=2) of autologous (n=6) transplantation for either acute leukemia (n=6) or neuroblastoma (n=2) after a conditioning regimen including total body irradiation (n=7) or a combination of Busulfan and Cyclophosphamide.Multiple OS were indentified in seven patients and a solitary OS in one. Locations included: clavicle (2), ribs (2), superior iliac epiphysis (1), metaphy-sis of the distal femur (2), distal (2) and proximal (1) tibia, proximal humerus (1), distal radii (3), scapula (3), proximal metaphysis of the proximal phalanges of the fingers (2) and parietal bone (1). OS were asymptomatic in four children. Eight lesions in five patients were resected and all were benign. No recurrence occured.Four children received growth hormone before diagnosis of OS, but there was no clinical, radiological or histological difference between those who did not. Univariate analysis showed an increased rate associated only with autolo-gous HSCT, with a 31,7% probability of a new OS et 12 years after HSCT.Ostoechondroma should be added to the other adverse effects of HSCT in children.