Atherosclerotic plaque burden has a strong correlation with plaque vulnerability. Three-dimensional (3D) volumetric assessment of atherosclerotic plaques has been suggested as an accurate method of quantifying plaque burden but has not been performed. In this study we use high-resolution magnetic resonance (MR) imaging to compare 3D volume differences of asymptomatic and acutely symptomatic carotid plaques (i.e. had cerebrovascular ischaemic symptoms within the previous 72 h of MR imaging). One hundred patients (46 acutely symptomatic and 54 asymptomatic) with atherosclerotic carotid artery disease underwent carotid MR imaging. Manual segmentation of plaque components was done to delineate lipid, fibrous tissue and plaque haemorrhage (PH). 3D-volume reconstruction of plaque components was done and used for comparison. Acutely symptomatic plaques had a lower normalized wall index and normalized volume index than the asymptomatic group (P = 0.04 and 0.01 respectively). Median percentage lipid volume was higher for asymptomatic plaques (28 vs. 5%, P = 0.004). However, the median percentage volume and prevalence of PH was higher in the acutely symptomatic group (P = 0.01 and 0.02 respectively). Acutely symptomatic plaques have less lipid content immediately after the acute event than asymptomatic plaques. This is most likely because of the escape of lipid-rich atheromatous debris into the blood stream at the time of plaque rupture. Due to this paradox, "high" lipid content of a plaque may not be a reliable feature of estimating its vulnerability immediately following the acute event. PH, which is prevalent and consistent in such plaques, may be a better indicator of plaque vulnerability during that period.