Anaphylaxis to insect stings has occurred in 3% of adults and can be fatal even on the first reaction. Large local reactions are more frequent but rarely dangerous. The chance of a systemic reaction to a sting is low (5% to 10%) in large local reactors and in children with mild (cutaneous) systemic reactions, and varies between 25% and 70% in adults depending on the severity of previous sting reactions. Venom skin tests are most accurate for diagnosis, but the radioallergosorbent test (RAST) is an important complementary test. The degree of sensitivity on skin test or RAST does not predict the severity of a sting reaction reliably. Venom sensitization can be detected in 25% of adults, so the history is most important. Venom immunotherapy is 75% to 98% effective in preventing sting anaphylaxis. Most patients can discontinue treatment after 5 years, with very low residual risk of a severe sting reaction.