Objective. To investigate of the prevalence of Cryptosporidium species in humans and calves in the province of Van, Turkey. Materials and methods. Included in this research were 150 patients, comprising 50 hemodialysis patients, 40 immunosuppressed patients with diarrhea, 30 patients with diarrhea only, and 30 immunocompetent patients. Collected were stool rectal samples from 50 calves that were housed in stables and farms in 10 central villages of Van, Turkey. Results. Cryptosporidium parvum was detected in 17.3% of the 150 human stool samples. C. parvum was observed in 20% of the 50 samples from the hemodialysis patients, 32.5% of the 40 samples from the immunosuppressed patients with diarrhea, and 10% of the 30 samples from patients with diarrhea only, whereas no Cryptosporidium spp. was detected in the samples from the immunocompetent patients. C. parvum was observed in only 6% of the samples from the diarrheic 30 calves. Conclusions. It was clearly understood that cryptosporidiosis was detected at a high rate in the samples from the immunosuppressed patients and those who were immunosuppressed with diarrhea, and that the active and effective species that causes cryptosporidiosis in the Van region is C. parvum. Hence, these patient groups should be evaluated in terms of cryptosporidiosis.