Anaphylaxis is a severe systemic allergic reaction with a rapid onset that is potentially fatal. The incidence of anaphylaxis is increasing. The diagnosis of anaphylaxis is based primarily on a detailed history-taking of the episode, including information about all exposures and events in the hours preceding the onset of symptoms. Target organ involvement is variable. In general, symptoms occur in 2 or more body systems: the skin and mucous membranes, upper and lower respiratory tract, gastrointestinal tract, cardiovascular system, and central nervous system. Epinephrine is the primary medical therapy, and it must be administered promptly. Intramuscular injection of epinephrine into the antero-lateral thigh is the preferred injection route in an urgent situation. Prevention of recurrence depends primarily on optimal management of patient-related risk factors, plus strict avoidance of the causative allergen or other triggers. When indicated, the practitioner should prescribe self-injectable epinephrine and should educate the patient on how to use it.