Vascular dementia (VaD) is a heterogeneous pathology currently regarded as the result of a variety of causes. Different types of VaD can be identified according to different criteria. This heterogeneity might be one of the causes of the controversial results observed, up to now, in clinical trials. Recently, the 10th revision of the International Classification of Diseases (ICD-10) explicitly identified subcortical VaD as a well-defined subgroup. Abnormalities of white matter are clearly detectable with computed tomography or magnetic resonance scans. The clinicoradiological association of dementia, blood hypertension, and other vascular risk factors, extensive white matter lesions, and small subcortical infarcts might be considered as a clinical univocal entity. Following the encouraging results of a preliminary pilot study, the above-mentioned criteria were followed to define a population of patients to be enrolled in a double-blind, parallel-groups, placebo-controlled clinical trial with nimodipine, which has been proposed as a drug that can improve cognitive functions in patients with VaD. The paper discusses the protocol design of this ongoing trial and its main entry criteria, with particular emphasis on the definition of the population to be enrolled. Implication for future trials in subcortical VaD are discussed further.