Adenocephalus pacificus (Cestoda: Diphyllobothriidae) is a fish foodborne zoonotic parasite whose stage of plerocercoid has been identified in marine fish. The objective of this study is to report for first time the infection by A. cf. pacificus in the anadromous Coho salmon, Oncorhynchus kisutch, from the Simpson River, Chile. During July 1997 and July 1998, the fish were examined for diphyllobothriidean parasites. The plerocercoids were found encysted in the stomach, peritoneum, liver, spleen, gonads, and muscles. The prevalence of infection fluctuated between 75.0 and 100% and the mean intensity was between 31.6 ± 25.4 and 34.9 ± 27.9 plerocercoids in July 1997 and July 1998, respectively. The frequency of plerocercoids in the muscles was 15.6 to 20.0%, respectively, and the mean was 0.3–0.4 plerocercoids/infected fish. Eight adult dogs were submitted to fecal exams and treated with a broad-spectrum antiparasitic. Six of 8 dogs were successfully orally infected by freshly obtained plerocercoids. Two of them ingested 40 plerocercoids, and we recovered between 34 and 32 cestodes at 21 and 27 d postinfection (DPI), respectively; we identified only 3 gravid specimens in the last dog and the rest of the worms were nongravid. The other dogs presented between 1 and 4 cestodes at 29 and 44 DPI. The prepatent period fluctuated between 21 and 28 DPI and the gravid cestodes measured between 24 and 104 cm long. Morphological identification of the studied adults was confirmed by light and scanning electron microscopy.