The study aim was to describe the management strategies used for severe infusion-related reactions (SIRs) and understand the impact of such events in oncology day hospitals in France, Germany, Spain, and the UK.The study was based on qualitative telephone interviews and quantitative self-completion questionnaires and asked healthcare professionals about the impact of SIRs and consequent actions taken.The procedures to prevent and manage SIRs were similar across countries and settings. In all countries, they were part of a larger risk-assessment and adverse events-prevention process. Preventive measures included patient history, risk assessment, pre-medication, and close monitoring of high-risk patients. The management procedures comprised stopping the infusion, triggering of the emergency chain, administering corticosteroids ± antihistamines, and hospitalization if necessary. The recalled SIRs had important consequences to affected patients, healthcare providers, and hospital organizational plans. All affected patients needed to be monitored closely for a prolonged time, thus blocking hospital beds. 44% of patients needed to be hospitalized, 17% needed resuscitation, and one patient died of cardiac arrest immediately after the start of the infusion. Importantly, 82% of patients were not re-challenged with the presumedly SIR-causing regimen or re-challenged in a later line.SIRs are unpredictable in nature, may have an extremely rapid onset, and are potentially fatal. Such events have a profound impact on the affected and surrounding patients, the care team and the organizational plan of the day-hospitals. Specific tools to reliably identify high-risk patients and predict the occurrence of events are needed.