Ataxia-telangiectasia (A-T) syndrome is an autosomal recessive chromosomal breakage syndrome caused by mutation of the ataxia-telangiectasia mutated gene manifested by progressive neurodegeneration, telangiectasias of sclera and skin, immune deficiency with sinopulmonary infections, and increased incidence of lymphoid malignancies and solid tumors. Three children with A-T underwent allogeneic stem cell transplantation (SCT) using protocols for Fanconi anemia. All 3 patients were engrafted with a mixed donor-recipient chimerism, but the full donor engraftment was observed in the T lymphocyte compartment. Immunologic recovery resulted in T cell production and lack of symptomatic infections. Regular intravenous immunoglobulin supplementation was needed until IgG production recovered, which depended on pretransplant serotherapy. During the observation period patients did not require hospital admission, and none of the transplanted patients developed sinopulmonary infections. Neurologic functions in reported patients were impaired and slowly deteriorated after transplantation, but no immediate toxicities were observed. The following hallmark features of A-T were present after SCT: neurologic symptoms, growth failure, telangiectasia formation, or increased serum alpha fetoprotein. SCT can help control immune deficiency constituting 1 of the features of A-T, and elimination of autologous hematopoiesis reduces the risk of lymphoid malignancies. Resolving crucial problems with qualification for SCT depends on balancing the risk and benefits of transplant therapy.