In order to understand the mechanism of clinical worsening in patients with cerebral infarction, attention was focused on the changes in cerebral angiograms obtained repeatedly before and after neurological deterioration. Among 212 stroke patients with minor neurological deficits, incomplete hemiparesis progressed to complete hemiplegia in 15 patients several days after the beginning of symptoms. On admission, 3 had internal carotid artery occlusion, 2 had stenosis of the internal carotid artery, 5 had occlusion of the middle cerebral arterial trunk, 2 had occlusion of the middle cerebral arterial branch, and 3 had no angiographically visible occlusion. The changes between the first and the second angiograms were of different varieties: another recurrent occlusion, progression of occlusion, new occlusion in the cerebral arteries opacified through the collateral pathway, recanalization of the initially occluded artery, and no change. Such different patterns of pathophysiological events show that the mechanism of neurological worsening in infarcted patients is not uniform. Based on the results from the present study, several problems which arose during the investigation and the somewhat vague definition of “progressing stroke” currently in use are discussed.