Before initiating antibiotic therapy, drug hypersensitivity is an important consideration, and a common strategy is to avoid giving patients medications when a high likelihood of severe reactions exists. With an increase in antibiotic resistance and a decrease in novel antibiotics, there is greater pressure to consider antibiotics in patients with a history of adverse reactions. The major concerns include IgE-mediated, or type I, reactions, anaphylaxis, Stevens-Johnson syndrome, and toxic epidermal necrolysis. Some antibiotics with similar characteristics, such as cephalosporins and penicillins, may be given safely to patients with a certain allergy profile. There is still greater concern when considering antibiotics for patients with reported allergy. Desensitization is a strategy to safely induce drug tolerance to a specific drug to limit the possibility of a type I reaction. © 2013 The Author 2013. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved.