In 50 patients with computed tomography-verified small, deep, lacunar, infarcts from a prospective stroke registry, we studied the lesion site in relationship with the clinical syndromes pure motor stroke, sensorimotor stroke and ataxic hemiparesis. Seventy per cent (95% confidence interval: 57-83%) of the lesions were located in the posterior limb of the internal capsule or adjacent paraventricular region, affecting the corticospinal tract in pure motor stroke, as well as the thalamocortical tract in sensorimotor stroke, and the cerebellar (dentato(rubro)thalamocortical and corticopontocerebellar) pathways in ataxic hemiparesis. This most frequently involved area is supplied by the anterior choroidal artery, indicating that this artery is the predominant deep, penetrating artery involved in small vessel disease causing lacunar stroke syndromes.