Omenn syndrome is a variant of SCID, inherited as an autosomal recessive disorder, and characterized by severe eczematoid dermatitis, eosinophilia, elevated serum IgE and a distinctive histology in enlarged lymph nodes. The etiology of Omenn syndrome is unknown, however, unlike other forms of SCID; patients with Omenn syndrome have activated T lymphocytes in their circulation capable of non-MHC restricted cytotoxic function. Recently, it has been observed that the use of immunosuppressive therapy, particularly cyclosporine, can modify the clinical manifestations of the disorder. Prior to the use of bone marrow transplantation this disease was universally fatal. Death typically occurred in infancy as the result of opportunistic infections and/or malignancies, most notably lymphomas. While bone marrow transplantation has become quite successful for many phenotypes of SCID, even with the use of alternative donors other than histocompatible siblings, in Omenn syndrome it remains a challenge. In our experience, patients with Omenn syndrome exhibit a higher incidence of Gram negative sepsis, before and during transplantation, and carry a significant risk of post-transplant rejection when compared with patients with other phenotypes of SCID. We report the results of six patients treated with bone marrow transplantation from alternative donors, three had unrelated donors (URD) and three had haplo-identical parental donors. Five of the six patients achieved complete and/or durable donor cell engraftment and only one patient experienced acute GVHD. Three patients died of transplant-related complications (infection or EBV-associated B cell lymphoma) between day +22 and day +95 post-transplant. Three patients survived more than 1 year post-transplant.(ABSTRACT TRUNCATED AT 250 WORDS)