Background. Bruxism is described as an orofacial parafunction that affects both children and adults. The maintenance of the childhood habit into adulthood may compromise health. As there are few studies on this issue, there is a need for further research on sleep bruxism among children. Aim. The aim of this study was to assess the prevalence of sleep bruxism in children and the influence of psychosocial factors. Methods. A cross-sectional study was carried out on 652 randomly selected children aged 7-10 years at public and private schools in Belo Horizonte, Brazil. The instruments used were: questionnaire for parents, Child Stress Scale, and the scales on neuroticism and responsibility from the prevalidated Big Five Questionnaire for Children. Psychological tests were administered and evaluated by psychologists. Sleep bruxism among children was reported by parents. The Social Vulnerability Index from the city hall database was used to determine the social classification of the families. The chi-squared test, binary and multivariate logistic regressions were used, with the significance level set at 5%. Results. A 35.3% prevalence of bruxism was found. No association was found between bruxism and stress, gender, age, or social vulnerability. The adjusted logistic model determined that children with high levels of neuroticism (OR = 1.9, CI 1.3-2.6) and responsibility (OR = 2.2, CI 1.0-5.0) are twice as likely to have the habit of sleep bruxism when compared to those who have low levels of these personality traits. Conclusions. A high degree of responsibility and neuroticism, which are individual personality traits, are determinant factors for the development of sleep bruxism among children. © 2009 BSPD, IAPD and Blackwell Publishing Ltd.