To determine Cryptosporidium spp. prevalence in faeces from asymptomatic sheep, 37 family flocks in Mexico State were sampled. Data were collected by the interview method and Ziehl-Neelsen stain of faecal samples for Cryptosporidium identification. The independent group proportion hypothesis test was used for differences in prevalences between sheep farms. A 34.3% general prevalence was found, and prevalence in herds with >100 animals was significantly higher (40.6%). Correlation was found between flock size and Cryptosporidium spp. presence (odds ratio, OR, 2.57; confidence interval, IC(95%), 1.84-3.60).