Allergic reactions are exaggerated or inappropriate immune responses to an antigen or allergen. There are four main types of allergic reactions which include humoral or cell-mediated immunity. Reactions may occur during the first episode of anesthesia, most frequently in the induction of general anesthesia. Although allergic reactions are not frequent events, their courses are unfortunately serious and life-threatening. The most severe form of an allergic reaction is anaphylaxis. The most prevalent symptoms of an allergic reaction are cutaneous, respiratory, and cardiovascular. Neuromuscular blocking agents (NMBAs) such as suxamethonium, atracurium and rocuronium, are consistently implicated as the group of drugs most likely to cause anaphylaxis. Latex is the second most common cause of anaphylaxis. Latex-induced anaphylaxis may occur in a variety of situations, all involving direct contact with latex, or with aerosolization of latex antigen adherent to the powder of latex gloves. The risk of an allergic reaction varies widely between different antibiotics. Some classes, such as beta-lactams, can cause both immediate and delayed reactions. Reactions to opioid analgesics are usually caused by direct mast cell mediator release, rather than IgE-dependent mechanisms. Intravenous and local anesthetics, colloids and blood products are less common causes of allergic reactions. The management of anaphylactic reactions that occur during general anesthesia is similar to the management of anaphylaxis in other situations. The treatment includes discontinuation of the presumptive drug, respiratory and cardiovascular support and administration of epinephrine, antihistamine and corticosteroids. The lack of an adequate diagnosis could lead to a potentially fatal re-exposure to the same agent. It is very important to identify and confirm the offending drug using ,,in vitro’’ or ,,in vivo’’ tests.