In ten patients, 11 infarcts involving mainly the internal capsule have been examined pathologically. Serial sections of the involved basal ganglia were studied in ten infarcts and only a gross dissection was made in the other. The implicated penetrating arteries were traced throughout their length and obstructive vascular lesions were found in nine instances. In two of the nine there was an atheromatous plaque with a superimposed thrombus, in four an atheromatous plaque had caused severe stenosis, in one a destructive arterial process lipohyalinosis had occurred, in one case the nature of the obstruction remained "uncertained," and in one the penetrating arteries were obstructed at their orifices by an atheroma in the superior division of the middle cerebral artery. In two cases the vessels were patent, suggesting embolism. The atheromas consisted almost exclusively of a conglomerate of fat-filled macrophages. The clinical correlate was a pure motor hemiplegia or hemiparesis involving the face, arm, and leg without sensory deficit, homonymous hemianopia, receptive aphasia, or apractognosia. Confusion was prominent in one patient.