Thymoma-associated immunodeficiency (TAI) is a rare, acquired adult-onset immunodeficiency. It includes the classic form of Good syndrome (GS), characterized by thymoma and hypogammaglobulinemia, as well as a non-classic form of GS. This condition leads to specific or combined deficiencies in both B- and T-cells, causing considerable morbidity and mortality, although the underlying immunopathology is still not well understood.