Whole-body extracts of Hymenoptera were used for diagnosis and treatment until controlled clinical trials proved them no better than placebo, whereas venom is 85% to 98% effective. Studies of natural history reveal why whole-body extracts were thought to work. The chance of future systemic reactions is low in large local reactors and in most children and varies between 20% and 70% in adults. Venom skin tests are most accurate, but RAST is an important complementary test. The degree of sensitivity on skin tests or RASTs does not reliably predict the severity of a sting reaction. Venom immunotherapy is recommended for patients at high risk for sting reactions. Rapid regimens are as safe as slower regimens. The recommended dose is 100 microg, but some patients require higher doses for full protection. Venom immunotherapy is continued every 4 to 8 weeks for at least 5 years in most cases. Skin test results become negative in only 25% after 5 years of therapy but in 60% to 70% after 7 to 10 years. When treatment is stopped after 5 years or more, there is a 10% chance of systemic reaction to each future sting, but most reactions are mild. Some patients have a higher risk of relapse and should continue treatment for an extended period.