Of 140 patients referred to the Pediatric Immunology Clinic during of 12-month period with the symptoms of recurrent infections or allergic respiratory illness, 21 (75%) were found to have selective IgA deficiency defined as serum concentration ≤ 5 mg. with normal levels of IgG and IgM. T lymphocyte number was reduced in the patients where as B cells with surface membrane IgA were increased. Autoantibodies and circulatory immune complexes were found more often in IgA-deficient subjects than in controls. Follow-up beyond the age of 9 years showed a spontaneous increase in serum IgA in 6, whereas 15 continued to have IgA deficiency. The latter group of children were characterized by more frequent infections, a higher prevalence of atopic disease, lower T cell count and serum IgG concentration, higher serum IgE level and a higher prevalence of food antibodies and immune complexes. These observations highlight the natural history and immunologic features of selective IgA deficiency.