Louse flies (Diptera: Hippoboscidae) are known as “flat flies” to wildlife rehabilitators. The University of Minnesota operates a Raptor Center in St. Paul, where staff rehabilitate large numbers of injured raptors submitted by citizens throughout the region. Staff at the center have noticed louse flies on many of their patients in previous years. The louse fly fauna of birds and mammals in the Upper Midwest was summarized in the 1940s, where museum records contained 9 species of louse flies from diurnal and nocturnal raptors. Arrival of West Nile virus in North America has increased interest in louse flies as potential vectors. The present descriptive study was undertaken to characterize the louse fly fauna on raptors admitted to the St. Paul Raptor Center.