Common variable immunodeficiency (CVID) is a common primary immnodeficiency disease, the hallmark of which is hypogammaglobulinemia. Due to the lack of antibodies, patients usually have recurrent bacterial infections, but there are a number of other puzzling manifestations, including inflammatory conditions, autoimmune disease, and the development of lymphomas. Most patients are diagnosed as adults, and delay in the recognition of the antibody defect is common. A number of defects of T cell function and deficits in the memory B cell pool have been identified, but the underlying cause of this defect remains unknown.