Angioedema is a diffuse swelling of the subcutaneous or submucosal tissues that occurs in both hereditary and non-hereditary forms. It can be a temporarily disfiguring condition, but not usually a serious one unless the airway is compromised. In the majority of cases, no underlying cause can be identified. In this report, a case of "idiopathic" angioedema that occurred while performing a periodontal surgical procedure is presented. This case is interesting because the patient was on long-term use of an angiotensin-converting enzyme [ACE] inhibitor for hypertension, and recent evidence has shown that ACE inhibitors suppress the breakdown of circulating bradykinins. With high plasma levels of bradykinins, a local anesthetic, periodontal surgical procedures, or even emotional stress may trigger an attack of angioedema. Practitioners should be aware of the pharmacologic side effects of ACE inhibitors and be prepared to handle an emergency if a patient's airway becomes compromised.