A 43-year-old male was admitted for reconstruction surgery to repair posterolateral rotatory instability of the knee. At the request of the surgeon, ranitidine was slowly administered intravenously immediately before the patient was transferred to the operating room to reduce the incidence of acid reflux. A few minutes later, during the transfer of the patient, anaphylaxis developed with hypotension, nausea, dyspnea, change in consciousness and urticaria. The patient had no previous history of any allergic tendency. After appropriate management, he recovered without complication. Following surgery, an allergic skin prick test was performed to determine if the patient was allergic to any of the drugs used during the surgery. According to the results, only ranitidine showed a positive reaction.