In a central institution for persons with mental retardation, the dental status in 30 adult patients with Down syndrome was compared with that in a carefully selected group of gender- and age-matched mentally retarded patients. This investigation showed an increased frequency of periodontitis in the population with Down syndrome. The caries rate, however, did not differ demonstrably between the groups. Edentulism was more frequent in patients with Down syndrome than in controls, and this fact may substantiate the observation of increased frequency of periodontitis. Caries seems to be less prevalent in institutionalized patients with mental retardation than in the population at large.