Angioedema is a rare, potentially life-threatening condition that has been associated with angiotensin-converting enzyme inhibitors since their introduction in the 1980s. The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), the largest antihypertensive study conducted to date, randomized 42,418 participants to a diuretic (chlorthalidone), a calcium channel blocker (amlodipine), an angiotensin-converting enzyme inhibitor (lisinopril), or an alpha-blocker (doxazosin). Patients who developed angioedema were compared for baseline characteristics and changes in antihypertensive drug administration. Fifty-three participants developed angioedema during active follow-up: 55% were black, 60% men, and 70% were assigned to lisinopril (including 62% of black participants with angioedema), 15% to chlorthalidone, 9% to doxazosin, and 6% to amlodipine. Six percent occurred within a day of randomization and 23% within the first week. Over half did not have an increase in their assigned (blinded) antihypertensive drug before angioedema onset; 3 (6%) had a dose increase within a week before onset. One patient died following an angioedema episode. The occurrence of angioedema in the angiotensin-converting enzyme inhibitor arm corresponds with previously reported angioedema-angiotensin-converting enzyme inhibitor associations.