Vaccine-preventable disease outbreaks continue to occur among undervaccinated populations in the United States, including contained religious communities. The Amish practice separation from the world through group solidarity and caring for their own. Amish religious doctrine does not prohibit vaccination; however, coverage levels for routine childhood vaccination remain low in many Amish communities. This report describes an outbreak of pertussis in an Amish community in Kent County, Delaware, during September 2004-February 2005, that resulted in 345 cases and affected primarily preschool-aged children. The outbreak underscores the need to promote vaccination in Amish communities through culturally appropriate strategies, such as education and outreach to community leaders.