Perioperative anaphylaxis can occur during or after surgery and can have life-threatening consequences. As anesthesia protocols become more complex and incorporate multiple agents to regulate physiologic processes intraoperatively, perioperative anaphylaxis is becoming increasingly recognized. The allergist should obtain detailed records from the anesthesiologist in order to perform appropriate testing to identify the likely causative agents. Testing should ideally be performed 4 to 6 weeks after the reaction to account for a refractory period after mast cell activation. This article includes 2 cases of perioperative anaphylaxis and reviews the historical elements that must be considered after a reaction has occurred.