The aim of our work is to examine the impact of lifestyle on body mass index, as well as to examine the impact of sociodemographic lifestyle factors in school children. Prevalence of overfeeding and obese children, is rapidly increasing both in the world and in our country, so obesity is gaining pandemic size. The research was conducted as a retrospective study for the period from 2011 to 2015. The respondents consist of 700 primary school students aged 7 to 14 from the territory of the municipality of Pancevo. The body mass index (BMI) - calculated on the basis of percentiles - is defined as a dependent variable in this paper ranks, categorized into four groups, as an independent variable are defined sociodemographic characteristics and lifestyle of young people. The questionnaire was formed for the purposes of this research, and dimensionality the questionnaire was confirmed by exploratory factor analysis. Between groups with different indexes body weight, there is a statistically significant difference in eating habits, leisure habits time and performing physical activity. Eating habits, leisure habits and physical activity, they are important predictors of body mass index, while school success is a predictor of lifestyle ages 7 to 14 years.