Background Plaque rupture and secondary thrombus formation play key roles in the onset of acute coronary syndrome (ACS). Multidetector computed tomography (MDCT) allows the non-invasive assessment of coronary artery stenosis and plaque properties. In this study, we investigated whether 64-slice MDCT could non-invasively detect a plaque rupture in patients with de novo angina. Methods and Results The study population comprised 67 patients with de novo angina. All patients underwent contrast-enhanced 64-slice MDCT and intravascular ultrasound (IVUS). Patients were divided into a plaque rupture group (n=27) and a non-rupture group (n=40) based on the IVUS. The 64-slice MDCT revealed that the prevalence of an ulcer-like enhancement space (37% vs 5%, p<0.01), a ring-like sign (41% vs 18%, p=0.04), in the plaque rupture group was higher than those in the non-rupture group. Maximum plaque thickness (2.1±0.9 mm vs 1.6±1.0 mm, p=0.04), outer vessel area (17.6±4.9 mm² vs 13.4±5.0 mm², p<0.01), percentage plaque area (82.3±9.1% vs 73.4±15.7%, p=0.01), and remodeling index (1.11±0.18 vs 1.01±0.15, p=0.04) of the plaque rupture group were all significantly larger than those of the non-rupture group. Conclusions The 64-slice MDCT can identify differences in lesion morphologies between ruptured plaques and non-ruptured plaques. From our results, the 64-slice MDCT might provide a useful tool for the non-invasive detection of plaque rupture. (Circ J 2008; 72: 1276 - 1281)