Background: The aetiology of cerebral small vessel disease is unknown. An association with endothelial dysfunction has been suggested. We systematically assessed all relevant studies of dynamic endothelial function in patients with lacunar stroke, as a marker of small vessel disease. Methods: We searched for studies of cerebral or peripheral vascular reactivity in patients with lacunar or cortical (i.e. large artery atheromatous) ischaemic stroke or non-stroke controls. We calculated standardised mean difference (SMD) in vascular reactivity, +/- 95% confidence intervals (CI) between small vessel disease and control groups. Results: Sixteen publications (974 patients) were included. In lacunar stroke: cerebrovascular reactivity (n=534) was reduced compared with age-matched normal (SMD -0.94, 95%CI -1.17, -0.70), but not age+risk factor-matched controls (SMD 0.08, 95%CI -0.36, 0.53) or cortical strokes (SMD -0.29, 95%CI -0.69, 0.11); forearm flow mediated dilatation (n=401) was reduced compared with age-matched normal controls (SMD -1.04, 95%CI -1.33, -0.75) and age+risk factor-matched controls (SMD -0.94, 95%CI -1.26, -0.61), but not cortical strokes (SMD -0.23, 95%CI -0.55, 0.08). Conclusions: Endothelial dysfunction is present in patients with lacunar stroke but may simply reflect exposure to vascular risk factors and having a stroke, as a similar degree of dysfunction is found in cortical (large artery atheromatous) stroke. Current data do not confirm that endothelial dysfunction is specific to small vessel stroke. Future studies should include controls with non-lacunar stroke.