(1) Atopy is common in subjects who experience anaphylaxis, regardless of its origin; (2) crustaceans and nonsteroidal anti-inflammatory drugs are the most common food and medication groups, respectively, thought to cause anaphylaxis; (3) causative agents can be identified for two thirds of the subjects, and recurrent attacks are the rule; and (4) subjects with idiopathic anaphylaxis are more likely to carry epinephrine for self-administration than those with identifiable causes.