Five hundred and seventy primary central nervous system (CNS) tumors from the Department of Pathology at the National Institute of Pediatrics in Mexico City, collected from 1970 to 1989, were histologically reclassified in order to find out their relative incidence as well as their outstanding features. With this, we could establish a frame of reference for our local population, contributing to the epidemiological analysis of these entities. All the tumors were examined independently by two pathologists (C.R. and M.R.), using the classification of Rorke et al. Histological type, patient age and sex, and tumor location were analyzed. CNS tumors were the secondmost frequently encountered solid tumors, after lymphomas, and were increasing in incidence at a rate of 2.2 annually. Children in the age group 0-9 years were most often affected, and there was a predominance of male patients. Astrocytoma and medulloblastoma were the most common tumor types. The infratentorial region was the most frequent tumor location in the 2- to 9-year age group. By contrast, in the under 2-year-olds a supratentorial location was more frequent, and the incidence of germ cell tumors was proportionally high. In general, some histological types seemed to be associated with particular age groups. Although we found primitive neuroectodermal tumors to be the fifth most common at all ages (except for medulloblastoma), many other authors do not report a similar finding.