During the period from August 1987 to July 1990, 241 fecal samples collected from 1 to 48 months old children with acute diarrhea and examined in the Child's Institute of Hospital das Clínicas of Faculdade de Medicina da Universidade de São Paulo, were submitted to parasitological tests in the Enteroparasitosis Section of the Instituto Adolfo Lutz. Fourty two (17.43%) fecal samples showed Cryptosporidium sp. oocysts by carbol-fucsin stain. Parasitism by Cryptosporidium sp. was more frequent during the period comprised from March to May, in the studied three years. The authors discussed the Cryptosporidium sp. in association with other agents.