The clinical condition known as vascular dementia remains poorly defined. Few studies have attempted a correlative link between the clinical syndrome and the structural abnormalities of the brain. Classically the clinical progression of the vascular dementing process is thought to be a multi-step process punctated by repeated episodes of ischemia, that are clinically expressed as strokes. In most instances it has been assumed that the substrate of vascular dementias consists of atherothrombotic infarcts. The objective of this report is to illustrate 3 cases of progressive (rather than stepwise) cognitive deterioration without clinical evidence of stroke, evolving over a period of several years, in which there were prominent vascular lesions. A complete autopsy and detailed neuropathologic examination demonstrated cerebral vascular lesions involving small arterial vessels (< 200 microns in diameter). The lesions consisted of moderate-to-severe arteriolosclerosis in two cases, and mild-to-moderate arteriolosclerosis in a case of Alzheimer's disease with severe cerebral amyloid angiopathy. Parenchymal lesions consisted of small cortical and subcortical infarcts, most of them smaller than 0.1 cm in average diameter, and subcortical leukoencephalopathy severe in two cases and mild-to-moderate in the third case. Severe atherosclerosis not accompanied by large infarcts was also present in one case. Arterial changes affecting small, distal branches causing sometimes small parenchymal lesions in association with diffuse cerebral white matter disease, appear to be the anatomical substrate that accompanies progressive cognitive impairment in some patients who are frequently diagnosed with Alzheimer's disease because in their clinical records there is neither history of strokes nor stepwise progression of symptoms.