WAS is a rare X-linked recessive disorder characterized by primary progressive T cell immunodeficiency, impaired antipolysaccharide antibody response, thrombocytopenia with small platelet, and eczematoid dermatitis. Untreated patients with typical WAS have poor prognosis with the major causes of death being infection, bleeding, lymphoproliferative disorders, and malignancy. Due to the increased risk of infectious and hemorrhagic episodes the best results with HSCT are achieved in patients less than five yr of age and are recommended as early as possible. Here, we report a three-yr-old boy with WAS who underwent UCB and BMT from his genotypically identical brother with Klinefelter syndrome.