Non-invasive assessment of plaque volume and composition is important for risk stratification and long-term studies of plaque stabilisation. Our aim was to evaluate dual-source computed tomography (DSCT) and colour-coded analysis in the quantification and classification of coronary atheroma. DSCT and virtual histology intravascular ultrasound (IVUS-VH) were prospectively performed in 14 patients. 22 lesions were compared in terms of plaque volume, maximal per cent vessel stenosis and percentages of fatty, fibrous or calcified components. Plaque characterisation was performed with software that automatically segments luminal or outer vessel boundaries and uses CT attenuation for a colour-coded plaque analysis. Good correlation was found for per cent vessel stenosis in DSCT (53 ± 13%) and IVUS (51 ± 14%; r2 = 0.70). Mean volumes for entire plaque and non-calcified atheroma were 68.5 ± 33 mm3 and 56.7 ± 30 mm3, respectively, in DSCT and 60.8 ± 29 mm3 and 55.8 ± 26 mm3, respectively, in IVUS. Mean percentages of fatty, fibrous or calcified components were 28.2 ± 6%, 53.2 ± 9% and 18.7 ± 13%, respectively, in DSCT and 29.9 ± 5%, 55.3 ± 12% and 14.4 ± 9%, respectively, in IVUS-VH. Significant overestimation was present for the entire plaque and the volume of calcified plaque (p = 0.03; p = 0.0004). Although good correlation with IVUS was obtained for the entire plaque (r2 = 0.76) and non-calcified plaque volume (r2 = 0.84), correlation proved very poor and insignificant for percentage plaque composition. Interclass correlation coefficients for non-calcified plaque volume and percentages of fatty, fibrous or calcified components were 0.99, 0.99, 0.95 and 0.98, respectively, and intraclass coefficients were 0.98, 0.93, 0.98 and 0.99, respectively. We found that using Hounsfield unit-based analysis, DSCT allows for accurate quantification of non-calcified plaque. Although percentage plaque composition proves highly reproducible, it is not correlated with IVUS-VH.