MHC class II deficiency (MHC Cl II Def.) is a rare primary combined immunodeficiency with severe evolution. Despite treatment with allogeneic bone marrow trasplantation (BMT), complete immunologic reconstitution has been rarely achieved in contrast to the results of BMT in other immunodeficiency. We describe the first italian patient with MHC Cl II Def. unsuccessfully treated with haploidentical BMT.