Cryptosporidium is an intracellular protozoan described since 1907 by Tyzzer. Cryptosporidiosis is a cosmopolitan disease, whose incidence is higher in summer and rainy season. The objective of this research was to report the prevalence of Cryptosporidium spp. in sheep from 4 commercial sites in 3 Municipalities in the State of Mexico, Mexico in summer. 200 stool samples were taken from pregnant, non-pregnant and nursing ewes and lambs under one year old. All sheep were clinically healthy. A general prevalence of 61% was observed. Texcaltitlán had the highest prevalence (70%). Ewes (63 %) had higher prevalence than lambs (55%). Nursing ewes showed the highest prevalence (67%), which represents a high risk for lambs.