In many studies vascular dementia (VaD) is the second most frequent cause of organic acquired cognitive dysfunction; accounting for 10% to 50% of the cases, depending on the geographical area, patient population, and diagnostic criteria used. There is growing evidence that VaD does not include only multi-infarct dementia (MID) but relates to complex interactions of different etiologies (risk factors, cerebrovascular disease), structural changes in the brain, host factors and cognition. This resulted in reconceptualization of VaD to emphasize the differences from Alzheimer's disease (AD). However, the diagnostic criteria used (DSM-IV, ICD-10, NINDS-AIREN, or ADDTC) are based on the experience with AD and as such have their limitations and are not interchangeable. From a regulatory point of view, therefore, future research is needed to better define VaD in general and possible subtypes of VaD as targets for drug trials. Methodological issues in VaD trials, as opposed to AD, will be emphasized. The European Medicinal Products Evaluation Agency (EMEA) has adopted a guideline for trials of symptomatic treatments of dementia, particularly in AD. There is no explicit guideline for VaD trials; however, many of the recommendations for AD are already applicable to VaD for drugs aiming at alleviating symptoms of dementia. On the other hand, VaD may be potentially preventable, underscoring the importance of primary and secondary prevention as in other cerebrovascular disorders. Large long-term trials are necessary to study the importance of different risk factors and possible intervention strategies with special reference to VaD.