Trichomonads found in pigs include the commensal Tritrichomonas suis (more well known because of its synonymy to Tritrichomonas foetus, a trichomonad parasite of cattle and other animals) and Tetratrichomonas buttreyi, which appear similar to Tritrichomonas suis under the light microscope. A trichomonad isolated from pig fecal samples was subjected to scanning and transmission electron microscopy for ultrastructural study. The organism's ultrastructure revealed features commonly found in trichomonads; however, features such as the number and length of flagella, type of undulating membrane, general body form, and shape and location of organelles such as the nucleus, Golgi complex, and hydrogenosomes indicated that the isolated trichomonad is not Tritrichomonas suis nor Tritrichomonas foetus. Polymerase chain reaction (PCR) corroborated these results. Moreover, the ultrastructure was similar to the ultrastructure of previously described tetratrichomonads. It is especially suggested that the isolate is T. buttreyi. These findings could be of significance in the differentiation among different porcine trichomonads in diagnostic procedures. In addition, this is the first known detailed ultrastructural study of T. buttreyi isolated from pigs; thus, this can serve as an aid for future comparison between porcine and bovine T. buttreyi.