OBJECTIVE To determine whether arterial wall hypertrophy in elastic arteries was associated with alteration in their mechanical properties in young patients with Williams syndrome.

RESULTS Systolic and diastolic blood pressures were higher in Williams patients (125/66v 113/60 mm Hg, p < 0.05). The mean (SD) intima–media thickness was increased in Williams patients, at 0.6 (0.07) v 0.5 (0.03) mm (p < 0.001). Normotensive Williams patients had a lower circumferential wall stress (2.1 (0.5) v 3.0 (0.7) mm Hg, p < 0.01), a higher distensibility (1.1 (0.3) v 0.8 (0.3) mm Hg⁻¹.10⁻², p < 0.01), similar cross sectional compliance (0.14 (0.04) v 0.15 (0.05) mm².mm Hg⁻¹, p > 0.05), and lower incremental elastic modulus (7.4 (2.0) v 14.0 (5.0) mm Hg.10²; p < 0.001).

CONCLUSIONS The compliance of the large elastic arteries is not modified in Williams syndrome, even though increased intima–media thickness and lower arterial stiffness are consistent features. Therefore systemic hypertension cannot be attributed to impaired compliance of the arterial tree in this condition.