Erythema marginatum is a characteristic skin rash seen in patients with hereditary angioedema (HAE); however, it can be confused with urticaria, leading to delay in correct diagnosis. The aim of this study was to clarify how often erythema marginatum is misinterpreted as urticaria, potentially leading physicians to refrain from testing for HAE. Few studies have been published on urticaria and prodromal symptoms in HAE, thus the incidence of these parameters were also investigated. A total of 87 patients affiliated to the national HAE Centre were included. Retrospective and prospective data on skin eruptions and prodromal symptoms were collected. Fifty-six percent of 87 patients had a positive history of erythema marginatum. Half of the patients had experienced erythema marginatum being misinterpreted as urticaria. The most prevalent other prodromal symptoms were other skin symptoms, malaise, psychological changes, fatigue and gastrointestinal symptoms. HAE patients with erythema marginatum have a longer diagnostic delay, presumably caused by misinterpretation of the rash as urticaria.