Background South Asians have a 1.5-fold increased stroke mortality compared with Europeans, despite similar blood pressures (BP). We hypothesized that it is the greater hyperglycaemia in South Asians that increases stroke risk, by adversely affecting cerebrovascular haemodynamics. Methods A population-based sample of 149 Europeans and 151 South Asians underwent metabolic profiling and concurrent measurement of finger BP using a Finapres and middle cerebral artery (MCA) blood flow velocity using transcranial Doppler ultrasound. Cerebrovascular autoregulation, cerebrovascular resistance [resistive index (RI) and pulsatility index (PI)] were calculated. Means of cerebrovascular haemodynamic measures were compared by ethnicity, with the introduction of explanatory variables to a regression model to determine which variable could best account for ethnic differences. Results Cerebrovascular resistance (RI) was 12.9?×?103 (0.9–24.8, P?=?0.04) greater in South Asians than Europeans. Systolic, diastolic and mean MCA velocities were also higher in South Asians (mean velocity 41.4?±?8.0?cm/s vs 38.0?±?8.0?cm/s, respectively, P?=?0.001). Low frequency gain, a measure of autoregulation, was worse in South Asians compared with Europeans (0.50?±?0.01?cm/s mm/Hg vs 0.45?±?0.01?cm/s mm/Hg, P?=?0.01). RI positively correlated with HbA1c (r?=?0.184; P?