Faecal samples from 804 cattle and buffaloes and 165 diarrhoeal children of Ismailia province were investigated by an immunochromatographic screening test and PCR to determine prevalences and distributions of Cryptosporidium spp. Results were analysed statistically for clustering of animal and human cases. Cryptosporidium herd prevalence was 73·3% and individual animal prevalence 32·3%. C. parvum was the dominant species in animals (65·7%). Young calves watered with canal or underground water were at particular risk of infection. Detection rates were higher when calves showed diarrhoea, fever and dehydration. Human Cryptosporidium prevalence was 49·1%. C. hominis dominated in humans (60·5%), followed by C. parvum (38·3%). Living in villages, drinking underground water and having contact with animals were risk factors. Cluster analysis revealed differences in the distribution of infections between animals and humans and suggests different transmission dynamics.