Experimental infections were established with Diphyllobothrium sp. plerocercoids obtained from Salmo gairdneri, a fish introduced at the beginning of the 1900s in the lake region of Chile. These permitted us to obtain adult parasites in Larus dominicanus and Canis familiaris. The histological features of the plerocercoids, their relation to the host, adult pattern and susceptibility of hosts allowed us to determine the presence of Diphyllobothrium dendriticum (Nitzch) for the first time in South America in the lacustrine region of southern Chile. It is believed that this cestode was introduced to this ecosystem by infected persons travelling from North America of Europe or, alternatively, brought by migratory birds, e.g., Sterna hirundo, S. paradisea or Larus pipixcan on their winter visits to South America.