Cryptosporidium parvum oocysts were detected in feces of dairy calves raised in Rio de Janeiro State and the risk factors involved in the infection were determined. A hundred calves aging up to 12-month-old from 13 dairy farms were sampled. Polymerase chain reaction was used to detect the presence of oocysts. The zoonotic C. parvum species was detected in 45% animals. Statistical risk factors analyses revealed an association between infection and animals raised in technical systems such as the use of milking equipment, milking cooler, and water trough (P<0.05).