Over a one-year period, based on a random cluster sampling design, 661 faecal samples from natural cases of diarrheic calves were taken in Fars province of Iran. The samples were taken from the 267 diarrheic calves of high and 394 diarrheic calves of average producing Holstein dairy cows. Faecal samples were collected directly from the rectum. Herd selection was based on geographical location and density of cattle in the region. Samples were collected based on 5 percent of herd population in 4 geographical regions: North, West, East and South of Fars province. The herds were stratified into small, medium and large size. Laboratory investigation consisted of a direct identification test for antigen of Cryptosporidium parvum. All herds had HPDC and APDC Cryptosporidium-infected diarrheic calves in their population. Diarrheic Cryptosporidium infected HPDC calves in southern region of Fars province were at much lower risk (P<0.05) than APDC calves. The rate of Cryptosporidium infection in diarrheic APDC calves in southern region of Fars province was highest when compared to other geographical locations. When considering the effect of age, diarrheic Cryptosporidium affected APDC Holstein calves of younger dams (>2 to 3years) showed a higher rate of infection when compared to diarrheic HPDC Cryptosporidium infected ones. There were no differences among the occurrence of Cryptosporidium infection in diarrheic HPDC and APDC calves of different herd size groups.