Background: Lacunar stroke (VaD-L) is the most common stroke subtype associated with vascular dementia (VaD). Objective: To evaluate the rate of cognitive and behavioral changes in patients with probable VaD-L. Methods: We measured rates of change on the Mini-Mental State Examination (MMSE), Digit Span, Logical Memory, Controlled Oral Word Association Test, CERAD battery and the Neuropsychiatric Inventory (NPI) of 77 [age at entry 65.9 +/- 8.1 (mean standard deviation) years] patients with probable VaD, periventricular white matter and basal ganglia lacunae, longitudinally studied for 25.7 +/- 11 months. Results: Mean number of follow-up visits was 2.6. Overall annual vascular event rate was 0.25. VaD-L in mildly and moderately impaired patients is characterized by progressive cognitive and behavioral decline. The rate of cognitive and behavioral progression depends on the occurrence of vascular episodes (VE) during the course of the illness [(-1.1) MMSE and (+4.0) NPI points annually without VE vs. (-2.0) and (+10.3) points following VE]. The rates of progression are a function of the severity of the cognitive and behavioral impairment. Impaired cognition is associated with impaired behavior. A subgroup of VaD-L patients runs a progressively deteriorating course despite the absence of clinically apparent new vascular episodes. Conclusion: VaD-L is characterized by cognitive and behavioral decline in 83% of the patients. The rate of decline is determined mainly by the severity of the cognitive and behavioral impairment at baseline and by the occurrence of new vascular episodes. (C) 2002 Elsevier Science B.V. All rights reserved.