The American White Pelican (Pelecanus erythrorhynchos) has been breeding at Medicine Lake National Wildlife Refuge (NWR) in northeastern Montana since 1939. We compiled information on the history and ecology of this breeding colony from U.S. Fish and Wildlife Service (USFWS) reports and narratives filed at Medicine Lake NWR. Nesting by American White Pelicans first occurred in 1939, and the recent 10-yr average size (1993-2002) is about 4,000 breeding pairs. Since 1990, the mean number of young fledged pair-1 was 0.51 ± 0.07 (SE, N = 56). Low temperatures, hailstorms, predation, and botulism have killed >50% of young pelicans in some years. American White Pelicans banded at Medicine Lake migrated south, mostly within the Central Flyway. They wintered predominately in Texas, Louisiana and Mexico. Protection of the Medicine Lake colony is important because the breeding colony is the largest in Montana and an important contributor to the eastern metapopulation.