Angioedema is a side effect that is often associated with the use of angiotensin-converting enzyme (ACE) inhibitor medications. These medications result in increased levels of circulating bradykinins. This case illustrates the result of a local traumatic event to the upper lip, presumably causing marked bradykinin release in a patient who was taking an ACE inhibitor. The local release of bradykinin from trauma, in addition to decreased bradykinin catabolism secondary to ACE inhibitor therapy, resulted in angioedema predominantly in the upper lip. The angioedema resolved with discontinuation of the ACE inhibitor. (J Am Board Fam Med 2008;21:577-9.)As the indications and usage of angiotensin-converting enzyme (ACE) inhibitor therapy increases, one of its potential side effects, angioedema, is becoming commonly encountered in primary care. Angioedema is a potentially life-threatening side effect of ACE inhibitor therapy, which has an estimated incidence of 0.1% up to 6%. 1 Angioedema resulting secondary to ACE inhibitor use may occur many years after therapy has been initiated. However, it most often occurs within the first week after starting therapy. 2 Up to 25% of reported cases of angioedema seem to be a result of ACE inhibitor therapy. 2 The other most common causes include allergic reactions, hereditary angioedema, C1 esterase inhibitor deficiency, and idiopathic angioedema. 2 The mechanism of action of ACE inhibitors includes the blockade of the ACE, which leads to vasodilation. Other actions of ACE inhibitors include blockade of the conversion of substance P to inactive peptides and the blockade of bradykinin degradation. The increase in circulating substance P and bradykinin, histamine release, and other mechanisms lead to vasodilatation and increased vascular permeability. 1-3 Angioedema does not resemble other forms of edema in that it does not appear in dependent areas and is often very transient and localized. 4 The most important risk factor for developing ACE inhibitor angioedema seems to be African-American race. The mechanism of this increased risk is not clear but may include bradykinin metabolism. Other risk factors include history of angioedema, allergies to seafood, and recent head or neck surgery. 2