Paranasal sinus infections can occur as a result of immunologic deficiencies, and may particularly involve local immune reactions. Other causes of sinusitis include allergic mechanisms which result in its occurrence in those diseases which are associated with allergy. The pathogenesis for sinusitis must be defined so that effective therapy can be directed toward underlying defects involved. Such treatment includes replacement therapy for insufficiencies of the immune system, elimination of antigens in hyperergic reactions, and antibiotics for bacterial infections.