Background: Recurrent and chronic infections of ear, nose, and throat (ENT) such as sinusitis (rhinosinusitis) and otitis media are one of the most common health care problems worldwide and significantly impact quality of life in both children and adults. Antibody deficiencies are the most common type of primary immunodeficiency and also the most likely to present with recurrent ENT infections. Methods: A study was carried out to search for underlying immunodeficiencies in 103 patients with recurrent or chronic ear, nose and throat infections. Serum total IgG, IgA, and IgM levels were measured by kinetic nephelometry, and IgG subclasses by enzyme-linked immunosorbent assay (ELISA). All patients were immunized intramuscularly with polyvalent pneumococcal vaccine (PENEUMO 23). Blood samples were drawn immediately before and 21 days after vaccination and antibodies to pneumococcal antigens were measured using a modified ELISA technique. Finding: Of 103 patients twenty one (20%) were found to have an immunodeficiency. One had a common variable immunodeficiency (CVID), 5 had selective IgA deficiency (one of them was associated with IgG2 deficiency and one with specific antibody deficiency). Eight patients had IgG-subclass deficiency including seven with an IgG2 deficiency and one patient with IgG3 deficiency. In 75 patients antibody titers of whole pneumococcal antigens were determined before and 21 days after immunization. Ten patients were found to have abnormally low antibody titers. Conclusion: The results of this study suggest that in a subpopulation of patients with a long standing history of ENT infections, a low serum immunoglobulin concentration or hypo responsiveness to pneumococcal antigen would be associated with susceptibility to recurrent infections.