Trap–neuter–release (TNR) programs, in which feral cats are sterilized and fed in unconfined colonies, have been advocated as a humane and effective way to reduce the impacts of feral cats on native wildlife. Little is known, however, about the effects of sterilization on feral cat movements and space use, particularly where colonies are located near natural areas. We determined home-range area and overlap and characterized the long-range movements of 14 sterilized and 13 intact radiocollared cats on Catalina Island, California, from 2002 to 2004. Male home ranges were significantly larger than those of females, but no significant differences were revealed in home-range areas or overlap between sterilized and intact cats. Cats regularly moved between natural habitats in the interior of the island and human-populated areas regardless of sex or treatment status, although most (68%; 17/25) of the cats that moved long distances were female. Island-wide, the cat population was estimated to be 600–750 cats, with >70% associated with developed areas, including existing TNR colonies. The influx of subsidized cats to natural habitats, combined with their high vagility and low trappability, makes TNR an unlikely solution for controlling feral cats on a large, rugged island like Catalina and, more generally, in other locations where human populations abut ecologically sensitive areas.