This is a prospective, international, multi-center, non-randomized, single arm, open-label, postmarketing study to investigate the formation of inhibitory anti-C1-INH antibodies in HAE subjects treated intravenously with Berinert. Individual treatment duration per subject is 9 months, irrespective of the number of treated attacks. All subjects will receive 20 IU Berinert/kg body weight per attack.