IgA deficiency is characterized by reduced (<0,07 g/L) or absent serum IgA levels. IgA deficiency is the commonest form of primary antibody deficiency and affects about 1 in 700 Caucasians. IgA deficiency is rare in some racial groups (Japanese, Africans). The majority of IgA-deficient in individuals remain free of infection due to the ability of IgG and IgM to compensate for the lack of IgA. Long-term studies have shown that a small proportion of IgA-deficient patients develop recurrent sinopulmonary or gastrointestinal infections. Most infection-prone-IgA-deficient patients have concomitant IgG2 subclass deficiency and a selective inability to produce antibodies against bacterial capsular polysaccharides. IgA deficiency is associated with an increased incidence of atopy, celliac disease, and a range of autoimmune diseases, including arthritis, “lupus-like” syndrome, autoimmune endocrinopathies, and autoimmune cytopenias.