Abstract Background and Objective CADASIL is the most common monogenic form of stroke and early onset dementia. We determined the prevalence of vascular cognitive impairment (VCI) in a cohort of CADASIL patients, and investigated which factors were associated with VCI risk, including clinical, genetic and MRI parameters. Methods Cognition was assessed in genetically confirmed CADASIL patients (n = 176) and healthy controls (n= 265) (mean(SD) age 50.95(11.35) v 52.37(7.93) years), using the Brief Memory and Executive Test (BMET) and the Montreal Cognitive Assessment (MoCA). VCI was defined according to previously validated cut-offs. We determined the prevalence of VCI and its associations with clinical risk factors, mutation location (EGFr 1-6 versus EGFr 7-34), and MRI markers of small vessel disease. Results VCI was more common in CADASIL than controls; 39.8 v 10.2% on BMET 47.7% v 19.6% of MOCA. CADASIL patients had worse performance across all cognitive domains. History of stroke was associated with VCI on the BMET (OR 2.12, 95% CI [1.05, 4.27] p = 0.04) and on the MoCA (OR 2.55 [1.21, 5.41] p = 0.01), after controlling for age and sex. There was no association of VCI with mutation site. Lacune count was the only MRI parameter independently associated with VCI on the BMET (OR: 1.63, 95% CI [1.10, 2.41], p = 0.014), after controlling for other MRI parameters. These associations persisted after controlling for education in the sensitivity analyses. Conclusions VCI is present in almost half of CADASIL patients with a mean age of 50. Stroke and lacune count on MRI were both independent predictors of VCI on the BMET.