AIM: The aim of the study was to evaluate whether socio-economic inequalities in the practice of physical activity existed among children and adolescents, using different indicators of socio-economic status (SES). SUBJECTS AND METHODS: Data were derived from the Italian National Health Interview Survey carried out in 2004-2005, which examined a large random sample of the Italian population using both an interviewer-administered and a self-compiled questionnaire. This study was based on a sample of 15,216 individuals aged 6-17 years. The practice of physical activity was measured on the basis of questions regarding frequency and intensity of activity during leisure time over the past 12 months. Parents' educational and occupational level, as well as family's availability of material resource, were used as indicators of SES. Multivariable logistic regression analyses were performed to estimate the contribution of each SES indicator to the practice of physical activity, adjusting for potential confounding factors. The results of the regression models are expressed as odds ratio (OR) with 95% confidence intervals (95% CI). RESULTS: About 64% of children and adolescents in the sample declared that they participated in moderate or vigorous physical activity at least once a week. After adjustment for gender, age, parental attitudes towards physical activity and geographical area, the practice of physical activity increased with higher parental educational and occupational level and greater availability of material resources. Children and adolescents whose parents held a middle or high educational title were 80% more likely to practice moderate or vigorous physical activity than subjects whose parents had a lower level of education (OR = 1.80, 95% CI: 1.40-2.33), while subjects with unemployed parents had an odds of practicing moderate or vigorous physical activity 0.43 times that of those children whose parents belonged to the top job occupation category (administrative/professionals). Socio-economic differences were about the same when the practice of vigorous physical activity only was considered instead of that of moderate or vigorous physical activity. CONCLUSION: Interventions that promote the practice of physical activity, and especially those aimed at the wider physical and social environment, are strongly needed to contrast socio-economic differences in physical activity among children and adolescents.