BackgroundGadopentetic acid is a common contrast agent for enhanced magnetic resonance imaging. Adverse reactions due to gadolinium-based contrast agents are rare and easily overlooked by medical staff. A patient developed a rash as the first symptom and quickly developed a severe allergic reaction after receiving gadopentetic acid. Patient presentationA 74-year-old female patient was admitted on January 11, 2022, for femur magnetic resonance imaging. At 12:05 pm, a routine intravenous rapid injection of gadopentetic acid (15 ml) was given. Two minutes after administration, the patient developed skin itching. No obvious rash was found, but a 10 mg intravenous injection of dexamethasone was given. Recount of eventsAfter 1 minute, skin pruritus had not improved significantly, saliva secretion had increased significantly, and a general discomfort appeared. At 12:10 pm, outside the scanning room, the patient suddenly became unconscious; 1 mg of EPINEPHrine was injected intramuscularly, and oxygen was given through a mask. Heart rate, blood pressure, and oxygen saturation steadily dropped. The patient was transferred to the intensive care unit. After EPINEPHrine, norepinephrine, terlipressin, and dexamethasone treatments, the vital signs eventually stabilized. The patient was judged to have had a grade III severe allergic reaction according to the first aid guidelines for severe allergic reactions in China. The patient was discharged from the hospital on the morning of January 14. ConclusionThis case stresses the importance of being equipped with the medicines, items, supplies, and equipment needed for emergency treatments in all departments where contrast agents are used. Patients with apparently mild adverse reactions to contrast agents should not be overlooked.