General anesthetics and contrast media can cause anaphylactic as well as anaphylactoid reactions. These events are of great concern to radiologists and anesthesiologists because of their relatively high prevalence, possible threat to life, and medical-legal consequences. Points discussed in this review are the critical evaluation of risk factors affecting prevention strategies, the need to be aware of pathogenic mechanisms relevant to prevention strategies, the use of alternative products if a culprit agent is known, the recognition of early signs of a reaction, the need to keep records of reactions on a patient's medical chart, the planning of prophylactic therapy, recommended actions after a reaction to an anesthetic or contrast medium, and the suggested establishment of allergy-anesthesiology centers to improve cooperation, and medical-legal issues. As any drug or contrast medium administered during general anesthesia or a diagnostic procedure can induce a potentially life-threatening or fatal event even in the absence of any evident risk factor in the patient's medical history or clinical status, we usually premedicate susceptible individuals at least to attenuate the severity of an unpredictable reaction, although we cannot rely on the efficacy of premedication to completely prevent a severe event. These recommendations, which are based on the literature and on the experience of our working group, aim to provide useful information for physicians and other specialists who operate in the absence of an allergy consultant.