During 2004-2005, contact with Salmonella-contaminated pet treats of beef and seafood origin resulted in nine culture-confirmed human Salmonella Thompson infections in western Canada and the state of Washington. This is the third published report of an outbreak of human illness associated with pet treats in North America and the first to describe such an outbreak in the United States. This report highlights the investigation of the outbreak by U.S. and Canadian public health officials and provides recommendations for reducing the risk that Salmonella-contaminated pet treats pose to humans. Public health practitioners should consider pet treats a potential source for Salmonella transmission.