We sought to examine the intravascular ultrasound (IVUS) findings of stent fracture. Stent fracture has been implicated as a cause of drug-eluting stent failure. IVUS is more likely to identify mechanisms of stent failure—including stent fracture—than angiography. Twenty stent fractures diagnosed by IVUS in 17 patients were evaluated. Eighteen stent fractures (90%) occurred in sirolimus-eluting Cypher stents, and 2 stent fractures (10%) occurred in bare metal stents, but none occurred in paclitaxel-eluting Taxus stents. Half of the stent fractures presented ≤1 year after implantation, and ½ presented >1 year after implantation. IVUS analysis showed that 9 stent fractures were complete (45%) and 11 were partial (55%); 10 (50%) were adjacent to stent metal overlap; and 5 occurred in a coronary aneurysm accompanied by malapposition (all Cypher stents) despite the absence of an aneurysm at index stenting. Compared with 60 matched control segments in patients without stent fracture, but with similar clinical events, the stent fracture group had longer stent segments (45.2 ± 23.0 vs 28.5 ± 14.9 mm, p = 0.003). Comparing stent fractures associated with an aneurysm (n = 5) with those that did not occur in association with an aneurysm (n = 15) showed that complete stent fracture was more frequent (100% vs 27%, p = 0.008), and all presented >1 year after index stenting (vs 33%, p = 0.03). In conclusion, IVUS is helpful to identify stent fracture as a cause of stent failure and to understand possible mechanisms of stent fracture such as aneurysm formation.