Atherosclerotic plaque progression is frequently accompanied by compensatory enlargement to preserve the lumen. These enlarging plaques develop features of vulnerability, however, leading to disruption and lumen obstruction. This complex transition from compensatory expansion to plaque disruption may not derive solely from progressive intimal disease. Concurrent changes at the intimomedial interface and within the tunica media and adventitia may play a role in plaque instability. We tested this hypothesis by investigating whether interface changes, including internal elastic lamina (IEL) rupture, and medial and adventitial changes, including inflammation, fibrosis, and atrophy, more frequently accompany disrupted than nondisrupted atherosclerotic plaques.