Immunoglobulin G4 subclass deficiency is the most common IgG subclass deficiency, followed by immunoglobulin G2 deficiency. However, IgG2 deficiency is the most common IgG subclass deficiency associated with recurrent infections. Immunoglobulin G4 subclass deficiency occurs in association with other isotype deficiencies. Isolated IgG4 deficiency, however, is much less common. Although respiratory tract infections are the most common manifestation in isolated IgG4 deficiency, other mucosal surfaces may also be affected in IgG4 deficiency leading to diarrhea and recurrent giardiasis. The authors herein report a case of isolated immunoglobulin G4 subclass deficiency in a young girl presenting with bronchiectasis. The diagnosis was established after ruling out other causes of secondary and primary immunodeficiency.