Local anesthetics are used throughout the health care system. In the perioperative setting and in other settings of exposure to local anesthetics, true allergy is reported very rarely. We present an unusual case of immediate-type perioperative hypersensitivity to lidocaine with cross-reaction to mepivacaine, which was missed on initial investigation. This case illustrates that lidocaine may be a "hidden allergen" in the perioperative setting and should always be considered a potential culprit in cases of suspected perioperative hypersensitivity. The case also demonstrates that suspected perioperative hypersensitivity requires highly specialized investigation and close collaboration between allergists and anesthesiologists.