To analyse the relationship between carotid plaque echolucency and cellularity.Carotid plaques (14 symptomatic and 16 asymptomatic) were snap frozen after endarterectomy and defined on the basis of their grey-scale-median (GSM), obtained from pre-operative high-definition ultrasonography, as either echolucent (or=32). DNA and total soluble protein were determined to assess cellularity.After correcting for wet weight, symptomatic plaques had significantly more DNA (0.400 +/- 0.07 vs 0.335 +/- 0.07 mg/g; p = 0.03) and soluble protein (34.1 +/- 6.6 vs 29.7 +/- 3.4 mg/g; p = 0.03) than asymptomatic plaques. Predominantly echolucent (Grey-Weale classification) plaques had more DNA (0.404 +/- 0.06 vs 0.332 +/- 0.08 mg/g; p = 0.03) than echogenic plaques. Plaques with GSM or= 32. Inverse relations were found between GSM and plaque DNA (r = -0.47; p = 0.02) and soluble protein (r = -0.45; p = 0.02) as well as between age and DNA (r = 0.39; p = 0.04) and soluble protein (r = -0.50; p = 0.003).Echolucency of carotid plaques as assessed by ultrasonography reflects plaque cellularity. This observation support the notion that ultrasonography can be used to identify high-risk plaques and evaluate effect of interventions on plaque structure.