We investigated the genetic structure and diversity of an endangered Canadian population of the Mormon metalmark butterfly (Apodemia mormo) using, for the first time, amplified fragment length polymorphism (AFLP) markers generated from non-lethal samples of butterfly wing tissue. Based on 326 loci, our analyses show a high degree of spatial genetic structure within the population, indicating limited gene flow, despite a small geographic range (\20 km). We found that geographic distance, particularly measured along valley bottoms, restricts gene flow within this population. However, other potential barriers to movement and genetic exchange were also identified, in particular urban development. Overall, the population exhibited low levels of genetic diversity. Future management should focus on increasing gene flow between the most isolated sub-populations, and through urban areas, by preserving and restoring as many habitat patches as possible.