Background Although anaphylaxis is recognized as an important life-threatening condition, data are limited regarding its prevalence and characteristics in the general population. Objective We sought to estimate the lifetime prevalence and overall characteristics of anaphylaxis. Methods Two nationwide, cross-sectional random-digit-dial surveys were conducted. The public survey included unselected adults, whereas the patient survey captured information from household members reporting a prior reaction to medications, foods, insect stings, or latex and idiopathic reactions in the previous 10 years. In both surveys standardized questionnaires queried anaphylaxis symptoms, treatments, knowledge, and behaviors. Results The public survey included 1,000 adults, of whom 7.7% (95% CI, 5.7% to 9.7%) reported a prior anaphylactic reaction. Using increasingly stringent criteria, we estimate that 5.1% (95% CI, 3.4% to 6.8%) and 1.6% (95% CI, 0.8% to 2.4%) had probable and very likely anaphylaxis, respectively. The patient survey included 1,059 respondents, of whom 344 reported a history of anaphylaxis. The most common triggers reported were medications (34%), foods (31%), and insect stings (20%). Forty-two percent sought treatment within 15 minutes of onset, 34% went to the hospital, 27% self-treated with antihistamines, 10% called 911, 11% self-administered epinephrine, and 6.4% received no treatment. Although most respondents with anaphylaxis reported 2 or more prior episodes (19% reporting ≥5 episodes), 52% had never received a self-injectable epinephrine prescription, and 60% did not currently have epinephrine available. Conclusions The prevalence of anaphylaxis in the general population is at least 1.6% and probably higher. Patients do not appear adequately equipped to deal with future episodes, indicating the need for public health initiatives to improve anaphylaxis recognition and treatment.