In order to design a dating system based on the microscopic picture of brain infarcts of recent onset, we performed the histological examination of 31 infarcts covering the first 4 weeks of evolution in 30 autopsy cases. The date of the cerebral vascular accident was clinically established in every case. There were 13 men and 17 women with a mean age of 65 years. Hemorrhagic infarcts were found in 15 cases and anemic infarcts in 16 cases. Based on the histological features four periods were identified: the first period, from day 1 through day 4, was characterized by the predominance of eosinophilic neurons and necrotic oligodendrocytes; the second period, from day 5 through day 7, differed from the first by the appearance of macrophages and of newly formed blood vessels; the third period, from day 8 through day 14, showed neuronal ghosts, macrophages, astrocytic proliferation, gemistocytes, and absence of neutrophils; and in the fourth period, from day 15 through day 27, there were no eosinophilic neurons, and neither necrotic oligodendrocytes nor myelin in the central portion of the infarct were identified. By assessing the histological features and accurately correlating the findings with the corresponding clinical data, we have been able to describe four distinct microscopic patterns of the first month of evolution of brain infarcts. The present findings may be considered useful morphological clues to better characterize the early evolutional phase of brain infarcts in humans.