The absence of B cells and a severe decrease in CD8+28+ cells were observed in two female children with CD4+ T cell lymphocytopenia. Idiopathic (primary) CD4+ lymphocytopenia is a rare entity and its pathogenesis and genetics are not yet known. The literature was reviewed, in particular for severe alterations in B and CD8+28+ cells and for the role of NF-kappa B and p56 (lck) in the immunopathogenesis. Whether the underlying mechanism in idiopathic CD4+ lymphocytopenia is found or not, these patients who present with severe symptoms of a combined immunodeficiency must be treated with intravenous immunoglobin regularly until they have a compatible donor for bone marrow transplantation.