Cryptosporidiosis is a widespread cause of diarrheal diseases of humans, young calves, and many mammals. Although in recent years molecular investigations on Cryptosporidium have increased, no data are available on Iran in this regard. Two species of Cryptosporidium are known to infect human beings; Cryptosporidium hominis which shows anthroponotic transmission among humans and Cryptosporidium parvum which shows zoonotic transmission between animals and humans. Cryptosporidium oocysts, morphologically identified as C. parvum, were isolated from 24 human and 35 bovine cases in Shahriar (suburb of Tehran, Iran), and genotyped by means of a Nested-polymerase chain reaction/restriction fragment length polymorphism analysis of the 18s rRNA gene. The isolates from bovine samples gave zoonotic or 2 genotype (C. parvum), and DNA profiles of human isolates gave two distinct genotypes, namely an anthroponotic or 1 (C. hominis) and zoonotic genotype or 2 (C. parvum).