We studied risk factors and presumed causes of infarct in 100 consecutive patients with a first stroke, who had an appropriate CT-proven infarct in the territory of the deep perforators from the carotid system (ITDPCS). The infarct involved the territory of the lenticulostriate arteries in 65 cases, the anterior choroidal artery in 23 cases, watershed zones between these two territories in four cases, and another territory in eight cases. In 42% of the patients, we felt the cause of the infarct to be small-artery disease. In 36%, at least one source of embolism was present (in 27% from the internal carotid artery, in 17% from the heart), either with (25%) or without (10%) associated hypertension (HT) and diabetes mellitus (DM). Other possible less common etiologies included migraine, syphilitic angiitis, and systemic diseases. We have confirmed that HT or DM are the most common etiologic factors of ITDPCS. However, large-artery disease and cardioembolism may be more important than previously assumed.