This cross-sectional study describes oral health problems in a sample of children with Down syndrome (DS) compared with their siblings. Data were collected using the Oral Assessment - Down Syndrome questionnaire, a validated French language evaluation to be completed by the child's carer. Parents attending a national meeting anonymously answered a questionnaire for their child with DS and for the sibling closest in age and returned their replies by post. Data concerning 204 individuals with DS (103 males, 101 females; mean age 9.6 years) and 161 of their siblings (80 males, 81 females; mean age 11.8 years) were returned. The association between DS status, age, and oral health was analysed. There was a greater frequency of oral health problems in those with DS with regard to function, clinical signs, disability, and development. The prevalence of chewing problems did not improve with age, the prevalence of bleeding gums and mouth breathing increased with age, and that of tongue protrusion reduced with age. Most parents rated the general and oral health of their children with DS highly, although worse than for their siblings.