['The incidence of post stroke cognitive impairment (PSCI) and predictive factors for PSCI among patients with acute lacunar infarcts is unclear.', 'To study the impact of acute lacunar infarcts and chronic white matter disease in the development of PSCI.', 'Prospective cohort study of stroke patients attending a tertiary neurology center. Patients with MRI confirmed acute lacunar infarcts without pre-existing dementia were recruited. Logistic regression was used to determine risk factors for developing PSCI.', '145 patients with a mean age of 55.8 years were studied of which 48 patients (33.1%) were identified to have PSCI. Patients with PSCI performed worse on the MMSE, MOCA and FAB and had significantly greater white matter hyperintensity (WMH) in the frontal subcortical (FSC) region (p = 0.006) and higher frontal subcortical acute infarct load (p = 0.002). Logistic regression demonstrated that deep subcortical WMH (odds ratio, OR = 1.45) and acute FSC infarcts (OR = 1.51) were associated with PSCI. High WMH load without acute FSC infarcts was associated with increased risk of PSCI (OR = 4.1). When patients developed acute FSC infarcts on pre-existing severe WMH, the risk of PSCI increased substantially (OR = 11.0).'] Is frontal subcortical ischemia crucial for post stroke cognitive impairment?