BACKGROUND: Evidence from epidemiological and neuroimaging studies suggests that cerebrovascular disease is associated with depressive disorders in the elderly, but the extent to which it contributes to the pathogenesis of late life depression is unclear. OBJECTIVE: To investigate the relation between cerebral haemodynamics and depression in a population based study, using transcranial Doppler ultrasonography. METHODS: Cerebral blood flow velocity and CO2 induced vasomotor reactivity in the middle cerebral artery were measured in 2093 men and women who participated in the Rotterdam study. All subjects were screened for depressive symptoms using the Center of Epidemiological Studies Depression scale, and those with a score of 16 or over had a psychiatric work up. In a semistructured interview, diagnoses of depressive disorders according to the DSM-IV and subthreshold depressive disorder were established. Analyses of covariance controlled for age, sex, stroke, cognitive score, and cardiovascular risk factors were used to compare means of haemodynamic variables. RESULTS: Subjects with depressive symptoms had reduced blood flow velocities (mean difference, -2.9 cm/s; 95% confidence interval (CI), -5.0 to -0.8; p = 0.008) and lower vasomotor reactivity (mean difference -0.5%/kPa; 95% CI, -1.0 to -0.05; p = 0.03). Blood flow velocity was reduced most in subjects suffering from a DSM-IV depressive disorder (mean difference, -4.9 cm/s; 95% CI, -8.5 to -1.4; p = 0.006). The overall reduction in vasomotor reactivity was accounted for by subjects with subthreshold depressive disorder. CONCLUSIONS: Depression in late life is associated with cerebral haemodynamic changes that can be assessed by transcranial Doppler ultrasonography. The observed reduction in cerebral blood flow velocity could be a result of reduced demand in more seriously depressed cases with a DSM-IV disorder, whereas reduced CO2 induced cerebral vasomotor reactivity is a possible causal factor for subthreshold depressive disorder.