The incidence of primary immunodeficiency diseases (PIDD) in Taiwan is estimated at 2.17 per 100,000 live births. This is much lower than in Sweden, with 8.4 per 100,000 live births. Patients with critical combined T-cell and B-cell immunodeficiency (CID) seem to be under-diagnosed because of delayed referrals to a tertiary care center which is able to organize a cooperative transplantation team encompassing, at least, a pediatric hematologist and a immunologist for severe combined immunodeficiency (SCID) classified as "pediatric emergency". Moreover, there are rare reported cases of adult-onset (over 18-years-old) common variable immunodeficiency (CVID). These cases are possibly treated as autoimmune diseases, but not PIDD. To date around the world, 206 kinds of PIDD have been found and 110 causal genetic effects were identified. Although epidemiological studies show wide geographical and racial variations in the prevalence and distribution of PIDD, we believe in Taiwan that those patients with Mendelian susceptibility to mycobacteria disease (MSMD), belonging to "congenital phagocyte defect", are often treated as isolated refractory mycobacterial infections or chronic granulomatous disease. Also, "diseases of innate immunity" and "autoimflammatory disorders" are not yet identified. To manage patients with hemophagocytic lymphohisticytosis syndromes, one of "disease of immune dysregulation, stem cell transplantation will be considered if there is poor response to chemotherapy. Patients with PIDD need better access to specialized clinical, laboratory and therapeutic resources.