This work describes the parasites and their respective pathologies in the stout razor clam, Tagelus plebeius (Lightfoot, 1786) (Psammobiidae) from Argentinean coasts. It represents the first report about a histopathological survey for these species in the Southwestern Atlantic. Specimens of T. plebeius were collected at Mar Chiquita coastal lagoon (37°46′S, 57°27′W) (n = 104 dissected under stereomicroscope, n = 28 histologically sectioned and microscopically examined) and from the mouth of the Quequén Salado River (38°56′S, 60°33′W) (n = 14 dissected under stereomicroscope). Tagelus plebeius was found housing two ciliate species without apparent host reaction and acting as first intermediate host for two digenetic trematode species of the families Fellodistomidae and Gymnophallidae, by hosting sporocysts (mainly in gonad and digestive gland that results in the replacement of host tissues) and as second intermediate host by housing a gymnophallid metacercaria. Likewise, T. plebeius was found parasitized by a larval spirurinae nematode encapsulated by hemocytes. The finding of two ciliate species, the gymnophallid cercaria and metacercaria, and the larval nematode represents the first record for the host. The Southwestern Atlantic populations of this clam seem to be devoid of serious pathogens in the study area.