Contaminated food sold by at least three locations of a restaurant chain in Arizona caused a prolonged outbreak of Salmonella Montevideo. Outbreak cases were first known in May and illness was confirmed through September. It was possible that outbreak cases actually began in 2007, but not confirmed. The outbreak strain of Salmonella Montevideo was isolated from samples of chicken collected from the restaurant outlets. There was evidence that raw chicken contaminated other food items and that the chicken was served undercooked. All 21 outlets of the chain restaurant received the contaminated chicken, however illness was associated mostly at three of the outlets, located in Maricopa County. Prior to this outbreak, these outlets were known to have poor food handling practices.