Adverse drug reactions (ADRs) can be divided into pharmacological ADRs (type A) and hypersensitivity reactions (type B). Type B reactions can be further subdivided into immediate (1 h, variable manifestation like exanthema, hepatitis, cytopenias). Prevention of hypersensitivity is often still a challenge.Selective literature search in Medline and Google Scholar as well as research in ADR databases like OpenVigil or SIDER.Laboratory tests ([specific] IgE, lymphocyte transformation test), histological examination, dermatological tests (prick tests, epicutaneous testing) and-under certain circumstances-provocation tests can be used for diagnostics. There are only a few pharmacogenetic biomarkers to predict hypersensitivity reactions. Currently, testing for defined HLA genes is mandatory before prescription of abacavir and before the use of carbamazepine in Han Chinese or Thai patients. Immediate discontinuation of the trigger is essential in all allergic hypersensitivity reactions. Immediate reactions are treated with antihistamines, glucocorticoids and occasionally with epinephrine. Delayed reactions are usually treated with glucocorticoids.Careful, structured diagnostics in case of suspected hypersensitivity together with adequate documentation (allergy passport) is necessary in order to avoid incidents in patients receiving subsequent treatment. Consistent use of existing resources (diagnostics and documentation) can help to avoid hypersensitivity reactions or to rapidly recognize and treat them, respectively.