<b><i>Background:</i></b> Nonlife-threatening headaches account for 3% of emergency department (ED) admissions, with social and economic negative consequences. We aim to investigate clinical features and risk factors of nonlife-threatening headache patients referring to ED versus those referring to headache outpatient clinics. <b><i>Methods:</i></b> During 6 months, we promptly reevaluated in our headache unit (HU) patients discharged from ED. We compared the clinical characteristics of patients who referred to ED with those of HU outpatients visited in the same time interval. Discriminant Function Analysis and Correspondence Analysis were used to determine risk factors for ED referral. <b><i>Results:</i></b> We recruited 49 post-ED patients and 126 outpatients. The main reasons for ED admission were poor response to acute treatment and aura-related symptoms. Headache diagnoses made in ED were generally not confirmed later (overall concordance of 47%), except for cluster headache (CH) and migraine with aura (MA). ED patients complained higher headache intensity, longer duration, and prolonged aura compared to outpatients. Aura was the main risk factor associated with ED admission on statistical models, while less prominent risk factors were sex, age, and years from migraine onset. <b><i>Conclusions:</i></b> ED patients presented a more severe headache clinical phenotype compared with outpatients. Headache diagnosis remains difficult in the emergency setting and is more easily achieved for the headache forms with standout features, such as MA or CH. According to statistical models, the aura is the most important risk factor for ED admissions.