This review addresses the most recent published literature regarding drug allergy, in order to provide physicians with a background for a better understanding of this problem of great relevance for public health.The sources of data for obtaining the original and review articles published in the last 10 years were MEDLINE, Pubmed and Lilacs. The articles chosen for this review relate drug allergy to immunological mechanisms, epidemiology, clinical and laboratory evaluation, skin lesions, clinical management, and re-exposure to the drug.Allergic reactions represent one third of adverse drug reactions. They are considered rare but with high morbimortality. Gell and Coombs' definition has been useful for classifying some types of drug allergic reactions; however, some still remain without classification because of poor knowledge of the mechanisms involved. The existence of T cell subpopulations with diverse characteristics reveals the complexity of the subject and, at the same time, elucidates several questions raised about it. It was recently postulated a new concept of chemically inert drug presentation to T cells, restricted to the major histocompatibility complex, but in a non-covalent and labile way. In clinical practice, without adequate laboratory tests, it is difficult to correlate clinical symptoms and immunological mechanisms. In vitro and in vivo skin tests have been employed in cases of suspected drug allergy reaction. However, there are very few commercially available reagents.Drug allergy constitutes an important problem in adverse drug reactions because of its potential of morbidity and mortality. It is necessary to emphasize the relevance of pharmacovigilance during treatment of patients, as well as the identification of possible immunological mechanisms involved in the events, through laboratory tests and detailed history and clinical evaluation.