Primary Immunodeficiency Diseases (PID) comprise inborn defects of the immune system which are and therefore difficult to study For this reason, the European Society for ImmunoDeficiencies (ESID) has set up an internet-based international patient and research database which integrates research data with more detailed clinical information. These disorders are not only found in children, but also in adults resulting in a wide range of clinical manifestations. Primary immunodeficiency adults are much less known and may remain undiagnosed.