Background. Insulin resistance is associated with hypertension. The relative influences of hyperinsulinaemia and high blood pressure on vascular hypertrophy and carotid distensibility is unclear in patients with longstanding hypertension. Methods. In 88 unmedicated patients with stage II-III hypertension and left ventricular hypertrophy on electrocardiogram we measured blood pressure, minimal forearm vascular resistance (MFVR) using plethysmography, intima-media thickness (IMT) and the wall distensibility of the common carotid arteries using ultrasound, and insulin sensitivity using a 2-h isoglycaemic hyperinsulinaemic clamp. Results. IMT was positively correlated to systolic blood pressure (r = 0.26, P < 0.05), whole body glucose uptake index (M/IG; r = 0.22, P < 0.05), age (r = 0.24, P < 0.05) and negatively correlated to body mass index (r = -0.24, P < 0.05); IMT did not correlate to fasting serum insulin (r = -0.14, NS). In men (n = 64) MFVR was positively correlated to systolic blood pressure (r = 0.30, P < 0.05), but was unrelated to M/G and serum insulin. The distensibility of the common carotid arteries was negatively correlated to systolic blood pressure (r = -0.40, P < 0.001) and in untreated patients (n = 22) positively correlated to M/IG (r = 0.47, P < 0.05). Conclusions. High systolic blood pressure was related to vascular hypertrophy, whereas hyperinsulinaemia and insulin resistance were not, suggesting that longstanding high blood pressure is a far more important determinant for structural vascular changes than insulin resistance at this stage of the hypertensive disease. However, hyperinsulinaemia and insulin resistance were associated with low distensibility of the common carotid arteries in the subgroup of never treated hypertensive patients. (C) Lippincott Williams and Wilkins.