The aim of this study is (1) to assess the incidence of suspected drug allergies in a pediatric hospital and the proportion in which these reactions are confirmed to be allergic; (2) to evaluate the diagnostic values of the different allergy tests available; (3) to investigate the pathophysiology of drug allergies, particularly by investigating the role of viruses, and by performing HLA typing and a gene expression profile both in the acute phase of the reaction and 2 months later.