Periodontal disease in Down's syndrome (DS) population seems to be a more common and serious problem than caries. The aim of this study was to assess the state of periodontal structures in patients with DS. The Community Periodontal Index of Treatment Needs was used for periodontal status assessment in 71 DS subjects aged 9-34 years. A control group consisted of 71 age- and sex-matched healthy individuals. Both groups were divided into three age groups: 9-15 (n = 24); 16-25 (n = 32); and 26-34 (n = 15) years. The results showed a similar percentage of subjects with bleeding and calculus. The intact periodontium was significantly higher in control than in DS (16.9% vs. none; p < 0.01). Deep pockets were more frequent in DS group than in the control group (14.1% vs. 1.4%; p < 0.01). The mean number of sextants with healthy tissue was lower, and of those with bleeding, calculus and shallow pockets significantly higher in DS patients than in controls (p < 0.01), so all DS subjects required some periodontal treatment (p < 0.01). It can be concluded that the severity of periodontal disease and the treatment needs seem to be significantly greater in DS than in healthy subjects.