Data sourcesPubMed, Embase, the Cochrane Library and reference lists of identified studies.Study selectionObservational studies comparing dental caries and body mass index (BMI) where BMI was clearly defined were considered.Data extraction and synthesisTwo reviewers independently abstracted data using standard forms with study quality being assessed using a modified version of the Agency for Healthcare Research and Quality (AHRQ) methodology checklist for cross-sectional studies. The weighted mean differences and corresponding 95% confidence intervals for dental caries between children with abnormal weight and those with normal weight were analysed.ResultsFourteen cross-sectional studies including 43,860 children (boys: 23,299; girls: 20,561) were included. Only two studies were considered to be of high quality, eight of medium quality and four of low quality. Four main patterns of associations between dental caries and BMI were found: five studies showed no association, five studies found a positive association, three an inverse association and one found a U-shaped pattern, which meant that the deft score was significantly higher in underweight children and there was a higher DMFT score in overweight and obese children.ConclusionsThis meta-analysis showed no differences in dental caries between underweight and normal weight children. Further studies are recommended using suitable sample sizes, to unify the criteria for BMI categorisation and the dental caries index, and investigate the confounding factors that might influence dental caries and BMI.