Acute attacks of hereditary angioedema are characterized by recurrent localized edema. These attacks can be life threatening and are associated with substantial morbidity and mortality. To determine factors associated with hospital admission of patients with an acute attack of hereditary angioedema presenting at the emergency department. This was a multicenter prospective observational study of consecutive patients (January 2011 through December 2013) experiencing an acute hereditary angioedema attack and presenting at the emergency department at 1 of 4 French reference centers for bradykinin-mediated angioedema. Attacks requiring hospital admission were compared with those not requiring admission. Of 57 attacks in 29 patients, 17 (30%) led to hospital admission. In multivariate analysis, laryngeal and facial involvements were associated with hospital admission (odds ratio 18.6, 95% confidence interval 3.9-88; odds ratio 7.7, 95% confidence interval 1.4-43.4, respectively). Self-injection of icatibant at home was associated with non-admission (odds ratio 0.06, 95% confidence interval 0.01-0.61). The course was favorable in all 57 cases. No upper airway management was required. Most patients attended the emergency department because they were running out of medication and did not know that emergency treatment could be self-administered. Risk factors associated with hospital admission were laryngeal and facial involvement, whereas self-injection of icatibant was associated with a return home.