A study was conducted on the occurrence of 2 Diphyllobothrium species in 5 species of fish from Lake Panguipulli in southern Chile and in dogs and humans associated with the lake. Fish were examined for plerocercoid larvae, and human and dog feces from the towns of Panguipulli and Choshuenco were sampled for the presence of tapeworm ova. Odonthestes (Cauque) mauleanum (Steindachner, 1896) is reported for the first time as a host for both Diphyllobothrium latum Linnaeus, 1758, and Diphyllobothrium dendriticum (Nitzsch, 1824). Basilichthys australis Eigenmann, 1927, is reported for the first time as a host for D. latum. Prevalences and mean intensities of D. latum and D. dendriticum were higher in introduced trout, Oncorhynchus mykiss (Walbaum, 1792), than in the native fishes, O. (C.) mauleanum, B. australis, Percichthys trucha (Valenciennes, 1833), and Galaxias maculatus (Jenyns, 1842). Prevalence and mean intensities of Diphyllobothrium spp. were similar (P > 0.05) in fish of both sexes. Intensities of infection by Diphyllobothrium spp. showed significant correlation (P < 0.05) with length in trout. Human infection by adults of D. latum was detected only at Choshuenco, with a prevalence of 2.8%. In this locality 12.5% of the people consumed smoked fish, showing a significant difference compared with Panguipulli, where 5.2% of the people consumed smoked or raw fish. No significant difference was detected in prevalence of infection in dogs in Panguipulli (1.8%) and Choshuenco (4.5%).