This study sought to determine the prevalence of bruxism in a Mexican community of children with Down syndrome, and to evaluate bruxism's relationship with age, sex, intellectual disability level, and type of chromosomal abnormality of trisomy 21. Using a cross-sectional design, 57 boys and girls (3 to 14 years old) were examined. Three approaches to establish presence or absence of bruxism were employed: parental questionnaire, clinical examination, and dental study casts. Data were analysed using bivariate analyses and conditional logistic regression. We found that the overall prevalence of bruxism was 42%. No statistically significant associations between bruxism and age, sex, or intellectual disability level were found. There was, however, a significant association between bruxism and type of chromosomal abnormality, with mosaicism being more frequently associated with bruxism. (Contains 4 tables.)