Epidemiological studies of periodontal disease have attempted to focus on defined groups in which the variables thought to be responsible for disease could be controlled or more easily identified. This study documents periodontal disease parameters in a unique population of Amish farmers. A total of 371 Amish were contacted and 282 were examined in their homes giving a participation rate of 76%. Ages ranged from 18 to 79 years. Overall means for periodontal conditions were 1.54 mm for attachment loss, 2.63 mm for pocket depth, 0.17 for calculus, 0.63 for plaque and 0.61 for gingivitis. One dental examiner conducted all examinations. Prevalence of periodontal disease tended to be higher among males and increased with age. The majority of Amish examined had little evidence of destructive periodontal disease; about 3.4% of teeth examined had attachment loss of 6 mm or more. These findings indicate a modest level of periodontal disease among the Amish. It is of interest that this population does not generally seek routine dental care. Preliminary analyses of health behavior data collected indicate a lack of regular oral hygiene practices. It appears that the Amish may have protective factors which affect their level of disease.