We investigated associations between Northern Mockingbirds (Mimus polyglottos) and the nest parasite Philornis porteri (Diptera: Muscidae), and how they vary with urbanization in northcentral Florida. Our goal was to ascertain if the ‘parasite-release’ hypothesis could contribute to high reproductive success of Northern Mockingbirds in urban areas. We collected 26 nests in 2007 and 73 in 2008 that had produced fledglings along an urbanization gradient, and measured the number of nests parasitized and the number of P. porteri in the nests. Habitats differed in prevalence of Philornis parasitism, but not directly in relation to urbanization. Parking lots and wildlife preserves had low levels of parasitism, whereas residential neighborhoods and pastures had significantly higher parasitism prevalence. Parasite prevalence was also significantly and positively affected by nest height and percentage of ground covered by buildings, trees, and open areas in the study site. Our findings do not offer strong support for the ‘parasite-release’ hypothesis in relation to urbanization, but suggest that vulnerability to parasites is habitat-specific.