We examined the mechanisms underlying the abrupt onset of the focal infarction in disseminated selective neuronal necrosis (DSNN) after temporary ischemia. Stroke-positive animals were selected according to their stroke-index score during the first 10 minutes after left carotid occlusion performed twice at a 5-hour interval. The animals were euthanized at various times after the second ischemia. Light- and electron-microscopical studies were performed chronologically on the coronal-cut surface of the cerebral cortex at the chiasmatic level, where focal infarction evolved in the maturing DSNN. We counted the number of neurons, astrocytes, and astrocytic processes (APs); measured the areas of end-feet and astrocytes; and counted the numbers of obstructed microvessels and carbon-black-suspension-perfused microvessels (CBSPm). Between 0.5 and 5 hours after ischemia, DSNN matured, with the numbers of degenerated and dead neurons increasing, and those of APs cut-ends decreasing; whereas the area of the end-feet and the numbers of obstructed microvessels increased and those of CBSPm decreased. At 12 and 24 hours after ischemia, the infarction evolved, with the area of end-feet and astrocytic number decreased; whereas the numbers of obstructed microvessels decreased and the CBSPm number increased. The focal infarction evolved by temporary microvascular obstruction because of compression by swollen end-feet.