Small-subunit (SSU) rRNA-based methods have been commonly used in the differentiation of Cryptosporidium species or genotypes. In order to develop a new tool for confirming the genotypes of Cryptosporidium species, parts of the 90-kDa heat shock protein (Hsp90) genes of seven Cryptosporidium species and genotypes known to infect humans (C. hominis, C. parvum, C. meleagridis, C. canis, C. muris, C. suis, and the cervine genotype), together with one from cattle (C. andersoni), were sequenced and analyzed. With the exception of C. felis from cats and C. baileyi from birds, the Hsp90 genes of all tested Cryptosporidium species were amplified. Phylogenetic analysis of the hsp90 sequences from all these species is congruent with previous studies in which the SSU rRNA, 70-kDa heat shock protein, oocyst wall protein, and actin genes were analyzed and showed that gastric and intestinal parasites segregate into two distinct clades. In this study, the secondary products of hsp90 produced after PCR-restriction fragment length digestion with StyI and HphI or with BbsI showed that parasites within the intestinal or gastric clade could be differentiated from each other. These data confirm the utility of the Hsp90 gene as a sensitive, specific, and robust molecular tool for differentiating species and/or genotypes of Cryptosporidium in clinical specimens.