Cotylophoron cotylophorum and Balanorchis anastrophus are the only amphistomes of ruminants that have been described so far in Argentina. Recent observations suggest that C. cotylophorum could have been misclassified. To confirm this, we examined specimens, collected in Corrientes Province and classified by Racioppi et al. (1994) as Cotylophoron cotylophorum, and re-classified these as Paramphistomum leydeni Näsmark, 1937. Flukes collected from Zárate (Buenos Aires) were also studied and compared against the former, resulting in the same species. The present study reports the existence of P. leydeni in Argentina, modifies the previous classification of C. cotylophorum and suggests that, based on the evidence of the amphistomes described so far, P. leydeni would be the most prevalent species in cattle of Argentina.Facultad de Ciencias VeterinariasCentro de Estudios Parasitológicos y de Vectores