I determined cause-specific mortality of yellow-bellied marmots (Marmota flaviventris) to assess the importance of predation as a mortality factor. Contrary to earlier findings based on visual observation, almost all (98%) mortality during the summer active season was caused by predation. Coyotes (Canis latrans) were the most important predators, followed by badgers (Taxidea taxus), American martens (Martes americana), black bears (Ursus americanus) and raptors, probably golden eagles (Aguila chrysaetos). Predation on marmots is cryptic; none of the predation events were observed and, in most cases, the marmot was consumed or removed so quickly and completely that searching for carcass remains would have been fruitless.