We report here a 6-month-old boy with severe congenital neutropenia (SCN) successfully treated by cord blood stem cell transplantation (CBSCT) from an unrelated donor. He had recurrent life-threatening respiratory infection due to severe neutropenia that was refractory to recombinant human granulocyte colony-stimulating factor (rhG-CSF). Because he had no HLA-matched sibling and no time to wait for unrelated donor, he received HLA-matched unrelated CBSCT as determined by DNA typing. A total of 6.4 x 10(7) CB nucleated cells/kg was infused after conditioning with busulfan/horse antihuman thymocyte serum/cyclophosphamide. No GVHD developed under the treatment with cyclosporin A and methyl prednisolone. The neutrophil count reached 0.5 x 10(9)/l on day 14, reticulocyte 1% on day 13 and platelet count over 50 x 10(9)/l on day 31. We conclude that unrelated CBSCT can be an indication for some cases of SCN, who have recurrent life-threatening infections and are refractory to rhG-CSF, and have no HLA-matched sibling.