Anaphylaxis under anesthesia is a rare but potentially severe disease. Although anaphylaxis is rare, it can be lethal if not diagnosed and treated appropriately. We present the case of a 43-year-old male with no prior allergy history who experienced a severe anaphylactic reaction that resulted in cardiac arrest after the intravenous injection of vecuronium. His surgery was postponed, and the patient required intensive care with ventilator support and other supportive measures. Post-reaction dermal sensitivity tests revealed a clear allergic reaction to vecuronium which confirmed the diagnosis retrospectively. Eventually, the patient made a full recovery and was rescheduled for surgery at a later date.