Endocrine evaluations after allogeneic Bone Marrow Transplantation in children are important to decide substitutive treatment and to prevent sequelae due to the conditioning regimen, Total Body Irradiation (TBI) and/or chemotherapy. We present a prospective study of evaluation after fractionated TBI with high dose AraC and Melphalan in leukemia or myelodysplasia in twenty two children. Endocrine deficit présent in all pts except one. Since BMT growth rate remained normal only in 2 pts. Growth velocity was decreased in 18 pts on year post BMT, 3 normalized their growth rate spontaneously. During the 2nd year, poor rates of growth were observed in 18 pts of whom 2 normalized their growth rate without treatment. Fifteen pts underwent two dynamic test for GH secretion; 11 of 15 had GH insufficiency (GH less than 10 ng/ml). Seven pts are substituted, two had just accepted the treatment, two refused. Gonadal hypofunction was present in 16 children, normal in 2, non explored in 4 because of age. Seven children showed evidence of compensated hypothyroïdism (raised TSH > 5 mU/l, normal T4, exaggerated peak TSH response). All seven are substituted by L-Thyroxine. Conclusion: Despite fractionated delivery of TBI, endocrine deficits are very frequent in pre pubertal periode and need long term endocrine review to propose substitutive treatment in affected children. Morbidity of such a procedure has to be born in mind to carrefully evaluate its benefice and danger versus chemotherapeutic conditioning regimens.