Thirty-five Florida panthers (Puma concolor coryi [Bangs, 1899]) collected from six counties in southern Florida between 1978 and 2003 were examined at necropsy for gastrointestinal helminths. The panthers were placed into two groups: 1) treated with anthelmintics (n=17), and 2) untreated (n=18). Nine species of helminths (one trematode, six nematodes, and two cestodes) were identified in the untreated panthers. The most prevalent helminths were Alaria marcianae (LaRue, 1917) (100%), Spirometra mansonoides (Mueller, 1935) (91%), and Ancylostoma pluridentatum (Alessandrini, 1905) (89%). Ancylostoma caninum (Ercolani, 1859) is reported from the Florida panther for the first time. The intensities of helminths with prevalences >10% did not differ between untreated panthers collected in 1978–1983 and 1996–2003. Treated panthers had helminth faunas similar to those of untreated panthers. The current anthelmintic treatment being used reduced the intensity of both A. marcianae and A. pluridentatum in panthers ≤6 mo posttreatment (PT); however, treated panthers between 6 and 9 mo PT, and >9 mo PT were similar to untreated panthers. Treatment was less effective on S. mansonoides and Taenia omissa Lühe, 1910. Treated panthers had slightly lower intensities of S. mansonoides at ≤6 mo PT; however, between 6 and 9 mo PT and >9 mo PT they had significantly higher intensities than untreated panthers. At all periods PT, the intensity of T. omissa for the treated panthers was similar to that of untreated panthers. We suggest that Mesocestoides sp. may not be present in the Florida panther population as reported earlier by Forrester et al. (1985), due to parasite misidentification by those authors.