Previously, amphibian malformations had only been studied at the site, state and regional levels, limiting our understanding of the types of malformations most commonly occurring in wild populations across the country. This study presents the results of radiographic analyses performed on morphologically abnormal amphibians collected from National Wildlife Refuges in 27 states and 6 of 7 US Fish and Wildlife Service regions. Despite considerable differences in species composition and ecological factors (e.g., habitat type, climate and land use), it was observed that abnormalities were remarkably similar across regions of the country. One regional difference that was noted was that higher proportions of forelimb and craniofacial abnormalities were observed in the western regions (regions 1 and 7) compared to the eastern ones. However, the uneven distribution of these abnormalities across sites, suggest that these elevated proportions may not be characteristic of region 1. Differences in species composition as well as in ecological factors such as habitat type and climate are potential explanations for this pattern in region 7. Given the known differences in regional causes, the results of this study suggest that these stressors may be affecting amphibian development in the same manner to produce primarily hindlimb reductions. Continued research comparing the types of abnormalities produced in different areas of the country as well as what stressors are present is essential to identify cause and affect relationships at sites hosting abnormal amphibians. / Department of Biology