Neuropathology of Alzheimer's disease (AD) demonstrates that the common occurrence of vascular lesions and vascular factors is suggested to contribute significantly to the clinical progression of the disease. This study has assessed the presence of vascular brain lesions and risk factors in subjects with diagnosis of AD and their influence on the disease course both in Late Onset Dementia (LOD) and in Early Onset Dementia (EOD). METHODS: MRI scans of 374 LOD and of 67 EOD patients were evaluated for the presence of vascular associated lesions and rated according to the age-related white matter changes (ARWMC) scale as "pure degenerative", "mixed" and "vascular" cases of dementia. Vascular risk factors burden (hypertension, diabetes, dyslipidemia, myocardial infarction) and disease progression were also assessed. RESULTS: 44% of LOD cases and 46% of EOD were classified as "mixed dementia cases". The vascular risk factors burden showed an increase from the pure degenerative to the pure vascular forms. Disease progression, calculated in two years using the Mini Mental State Evaluation (MMSE), Activities of Daily Living (ADL) and Instrumental Activities of Daily Living (IADL) scores, did not reveal differences among the three different classes of dementias. CONCLUSIONS: Vascular lesions are found in the majority of LOD cases and in about one half of EOD. This observation is consistent with the hypothesis of a synergistic effect of the degenerative and vascular factors on the development of cognitive dysfunction. The linear increase of the vascular burden supports the idea of a continuum spectrum between the pure degenerative and the pure vascular forms of adult-onset dementia disorders