X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection and neoplasia is a rare combined T and B cell immunodeficiency characterized by recurrent sinopulmonary and viral infections, persistent elevated Epstein-Barr virus (EBV) viremia and increased susceptibility to EBV-associated B-cell lymphoproliferative disorders. Immunological analyzes show normal lymphocyte count or mild to moderate lymphopenia, inverted CD4:CD8 T-cell ratio and hypogammaglobulinemias.