Piroplasms isolated from a farmed reindeer and elk in Wisconsin were determined to be Babesia odocoilei, based on morphology and ribosomal RNA (rRNA) analysis. Different clinical manifestations were observed in the two host species. The reindeer was parasitemic and exhibited acute babesiosis resulting in death, while the elk showed no parasites in blood smears and no overt clinical signs of babesiosis. B. odocoilei was, however, readily cultured from elk erythrocytes. Small subunit rRNA gene sequences from the two isolates were identical to that previously reported for B. odocoilei. Internal transcribed spacers 1 and 2 and 5.8S rRNA sequence analysis showed an overall identity range of 94.3-98.1% to corresponding sequences from three previously reported B. odocoilei isolates, but the Wisconsin reindeer B. odocoilei shared only 87.3% identity with a previously reported Babesia sp. isolated from a reindeer in California (RD61).