Several case reports of involvement of the nervous system by Paracoccidioides brasiliensis have been published, changing thus the concept that the nervous system would no be adequate to the proliferation of this fungus. In the material of the Department of Pathology of the University of São Paulo Medical School, collected up to September 1964, 145 cases of paracoccidioidomycosis were found. In 14 of them there were lesions of the nervous system, giving an incidence of 9,65%. This high incidence contradicts the frequent assumption that the involvement of the nervous system in cases of South American blastomycosis is exceptional. In our material most of the cases of neuroblastomycosis had not systemic lesions, 2 of them having isolated involvement of the nervous system. This fact does not agree with the frequent observation of patients with lesions in all organs but the nervous system. There are no pathophysiologic reasons to explain such contradiction, but it can be assumed that individual conditions, in some cases, make the nervous system vulnerable to the parasite. Of the 14 cases studied, 5 had lesions of the meninges and 9 had gra-nulomata of the brain. Of the 5 cases with meningitis, 3 had an isolated basilar leptomeningitis; in 1 case lesions of the pia-arachnoid of the brain convexity were also found, and in another one the spinal meninges were also involved as well the spinal roots. The granulomata of the brain were isolated in 5 cases and multiple in 4. The most frequent site of the lesions was the cerebral hemispheres (6 cases); in 2 cases the cerebellum was involved; the thalamus, pons and medulla were involved in one case each. This predominance of the hemispheric localization must be related to the larger blood supply of this parte of the nervous system, owing to the hematogenic route followed by the parasite. In our material no lesions of the spinal cord were found. However, no definitive conclusions can be drawn, as there was no systematic study of that parte of the nervous system. From a histopathologic viewpoint the meningeal inflammatory lesions were of the productive type, with a nodular or diffuse distribution. The characteristic cellular elements of this process are the gigantocytes of the Langhans type, the histiocytes, lymphocytes and plasmocytes, the two latter showing a predominant perivascular distribution. In the nodular forms there is a trend to the confluence of the granulomata and focal zones of caseous or gummous necrosis can be found. Arterites also can be found, causing degeneration of the nervous structures. The Paracoccidioides brasiliensis are generally abundantly found either free or phagocyted by histiocytes or gigantocytes. The inflammatory infiltrate grows along the Virchow-Robin's spaces, reaching the outer layers of the nervous parenchyma. The parenchymatous forms present a large central necrotic areas, with the characteristics of caseous or gummous necrosis, surrounded by histiocytes, gigantocytes, lymphocytes and plasmocytes. Fibroblasts and collagenous fibers surround and limit these granulomata of the encephalic parenchyma. Arterites are also observed and seem to play an importante role in the necrotic processes. The fungi are generally abundant, being found especially at the periphery of the necrotic areas or within the inflammatory tissues, free or phagocyted by histiocytes. In the nervous tissue neighboring the granulomata various degrees of degenerative processes of the neurons and glia are observed, as well as hyperplastic reaction of the oligodendroglia, microglia and astroglia. The inflammatory reaction of South American blastomycosis of the nervous system is not specific and, by itself, does not permit the etiologic diagnosis of the process. Only the finding of the parasite, with its characteristic forms, make it possible to establish the cause of the lesion.