Background: The occurrence of prodromes has been associated with swelling in hereditary angioedema (HAE). The aim of the study was to analyse the frequency of prodromal signs, the level of awareness among HAE patients and to understand the actions taken by patients when they experienced them. Methods: An online survey to assess patient experiences of prodromal symptoms was conducted among 208 HAE patients from the UK and Spain. Results: 60% of HAE patients who experience prodromes can always or usually predict an impending swelling. Almost 40% of participants noticed prodromes within the 2 hours preceding an HAE attack. Tiredness/fatigue (64%), pressure or tightness in the skin (53%) and abdominal pressure (52%) were the most reported early symptoms. C1-esterase inhibitor (C1-INH) and icatibant were prescribed to 75% and 65% of participants, respectively. 56% of participants in the UK reported self-medicating at the time of prodrome, whereas 65% of patients in Spain preferred to wait or relax when early symptoms began. 30% of patients said they usually took their medication within 1 hour of experiencing the prodrome. The percentage of patients who needed only one injection to treat the attack increased when patients took their medication early in the prodrome (from 55 to 66%). Conclusions: The majority of patients who have early symptoms were usually or always able to predict that a swelling would occur. Early treatment of HAE attacks is associated with less medication usage, but there is still no common understanding of what ‘early treatment’ means.