Objectives: Low glycaemic index (GI) diet is associated to prolonged sense of satiety and lower daily food intake frequency. This study was aimed at investigating the association between GI of breakfast (bGI) and caries prevalence. Methods: 704, 3-to-5-year-old children (mean age, 4.2±0.8; M/F ratio=0.98) were clinically examined at school according to WHO procedures and the d3f teeth were recorded. A 24-hour recall of children's dietary intake was conducted interviewing the caregivers, who also provided information on other caries-related anamnaestic variables. bGI (dichotomised between low/high arbitrarily choosing 50.4 as cut-off point) and daily intake frequency of cariogenic (i.e., rapidly fermentable) carbohydrates between main meals (fermCH) were calculated. Odds ratios (OR) for presence of at least 1 d3ft were calculated and statistically analysed by means of chi-square test (crude OR, cOR) and logistic regression analysis, using d3ft=0/d3ft>0 as explanatory variable (adjusted OR, aOR). The variables associated to fermCH were also analysed using multiple regression. Results: Subjects with d3ft>0 were 18.2% (128/704), mean d3ft was 0.6±1.8, mean bGI and fermCH were relatively low (52.0±6.2 and 1.2±0.9, respectively). Children with low bGI had significantly lower energy intake at breakfast (194.3±98.4 vs. 286.8±75.8 Kcal, t-test=14.1; p<0.0001; overall mean, 236.0±107.3 Kcal). cORs and aORs were 2.0 (95CI, 1.3-3.0) and 1.6 (95CI, 1.1-2.5) for bGI, 1.6 (95CI, 1.3-2.0) and 1.5 (95CI, 1.2-1.9) for fermCH. Statistically significant aORs for age (1.5, 95CI, 1.3-1.7) and immigrant background (2.6, 95CI, 1.1-5.6) also were found. High bGI, low mother's educational level, immigrant background were directly associated to fermCH. Conclusions: High bGI may increase caries risk for at least two reasons, firstly, a high bGI is rich in fermentable carbohydrates and, therefore, meals with high GI are per se cariogenic. Secondly, because high GI meals abbreviate the duration of satiety, consequently increasing children's demand for food, possibly, not necessarily, cariogenic food.