Tramadol is frequently used to treat postoperative pain and is generally considered safe. In this case, anaphylaxis due to intravenous tramadol is presented. Left knee arthroplasty was performed on a 75-year-old patient with hypertension using an angiotensin-converting enzyme (ACE) inhibitor. The patient was administered 100 mg of tramadol for postoperative pain. Itching and redness, dyspnea, respiratory arrest, and cardiovascular collapse occurred in the patient within 1-2 minutes. The service team announced code blue, and 100 mg of methylprednisolone and 45.5 mg of pheniramine were administered intravenously with rapid fluid resuscitation. Spontaneous breathing started within 5-6 minutes of the patient who was given positive pressure ventilation, and hemodynamic recovery was observed without the need for adrenaline administration. Anaphylaxis should be kept in mind when administering tramadol, especially in patients using ACE inhibitors. It is vital to recognize anaphylaxis quickly and to start the follow-up and treatment of patients.