The purpose of the study was to determine the reliability of ultrasonography in assessing plaque pathology and to relate it to clinical symptoms. Ten symptom-free patients and 26 with symptomatic carotid plaques with a stenosis > 70%, as detected by arteriography, were assessed by duplex. The findings were compared with the clinical presentation and plaque pathology. Pathological specimens of the plaque that had < 60% fibrous tissue were associated with an increased incidence of past stroke (P = 0.002). Plaque ulceration, haemorrhage and calcium were all unrelated to the clinical presentation. Using the pathological specimen as the 'gold standard', ultrasonography was unable to detect plaque ulceration or haemorrhage. Plaque regularity, irregularity, homogeneity and heterogeneity were not consistent with plaque pathology or the clinical presentation. The fibrous tissue was significantly greater (73%) in plaques with an echogenic character compared with those with an echolucent morphology (63%; P = 0.04). Moreover, echolucent plaques were most common in symptomatic patients and echogenic plaques in symptom-free patients (P = 0.002).