Common variable immunodeficiency is a complex primary immuno-deficiency disease that has as its hallmark subnormal amounts of at least two of the three main serum immunoglobulin isotypes. About 45% of cases are diagnosed before the patients reach 21 years of age, but the time of diagnosis may be delayed until even the sixth or seventh decade of life. The main clinical manifestations include sinopulmonary or gastrointestinal infections, autoimmunity, and neoplasia. The molecular defects of this disease are unknown and may involve intrinsic B-cell or T-cell defects, or both. At present, the mainstay of treatment is intravenous immunoglobulin, but experimental methods have shown that other in vivo methods might ultimately be found to ameliorate this immune deficiency disease.