Aim: The aim of this study was to determine the influence of the eating habits, dental caries and the socio-economic status on the body mass index (BMI) in children aged 1 to 16 years. Methods: It is a descriptive study conducted on 220 children who consulted the department of paediatric dentistry of Monastir from January 5th to March 6th, 2016. After measuring the height and weight of each child, an oral examination was performed. A questionnaire was filled concerning the demographic data, eating habits and oral hygiene. Results: Children belonging to the age group between 6 and 12 years represented 66.3% of the sample. Children coming from a modest socio-economic status represented 61.4%. Those coming from an urban area accounted for 76.6%. Almost all the children (94.4%) have snacks and 57.5% of them nibble. The frequency of tooth brushing was once a day for 42.9% of the children. The calculation of BMI showed that 86.9% of the children were thin. The mean DMF index was 4.14% and it was higher in children less than 6 years old and in underweight children (p 0.05). The BMI was influenced by the living environment and the frequency of sweets consumption. Conclusion: This study showed the relationship between the weight and height deficit, the high number of dental caries and the eating habits of the children. Nibbling and frequent sweets intake, which maintain a constant acid pH in the oral cavity, increase the carious risk while ensuring a feeling of satiety that results in a deficient BMI.