Objective: This study aimed to determine the prevalence of periodontal disease among children and adolescents with Down syndrome and the possible repercussions of such pathology in the quality of life of the group in question. Method: The sample consists of 93 individuals with Down syndrome 6-20 years old, living in Brazil (Minas Gerais). Periodontal probing was carried out on every site of each tooth. The Plaque Index and periodontal clinical parameters were recorded. A broad interview was carried out with the mothers, which consisted of an adaptation of the Oral Health Impact File OHIP-14 that was used to measure the negative repercussions of periodontal disease in the daily lives of these individuals. Results: The prevalence of gingivitis was 91%, whereas periodontitis was found in 33% of the individuals. When the impact of periodontal disease on the quality of life was correlated with the clinical periodontal parameters, it was observed that there are significant statistical differences among them: bleeding on probing, probing depth and attachment loss. These same results, correlated with all the different groups that are categorised according to the diagnosis of periodontal disease, also show significant differences. Conclusions: Periodontal disease can be considered as a condition with high prevalence within the group in question, which has negative effects on the quality of life of the subjects. These effects are aggravated by the seriousness of the disease. (Contains 2 tables and 1 figure.)