A randomized stratified sample of 522 children attending the third class of primary schools within the area of Bologna Local Health Unit was analysed for physical activity and sports practice. Information about the children's habits and availability of facilities for physical and sports activities were collected by means of structured questionnaires completed by children (507 respondents), parents (491), reference teachers for physical education (26) and class teachers (46) during the school year 2006-07. At the same time, the children's heights and weights were measured in order to calculate BMI values. Regular sports activity is practised by 80.1% of children (males: 82.4%, females: 77.6%), with significant diferences between genders only in children with at least one non-Italian parent (M>F, p < 0.05); the practice of sports is influenced by the area of residence (metropolitan > plain and hills, p < 0.05) and nationality (Italians > non-Italians, p < 0.01). Children with at least one actively sports practising parent are involved more frequently in sports activities (p < 0.001). In free time, sedentary activities are prevalent for both sports-practising children and not. However children not involved in regular sports activities tend to practise outdoor physical activities with a frequency significantly higher than children involved in sports (17.3% vs 10.4% of respondents). The percentage of completely sedentary children, who stated that they practise neither sports nor physical activity in their free time, is 7.3% (metropolitan area: 4.5%, hills: 8.7%, plain: 10.6%). The prevalence of overweight is 24.4%, of obesity 9.7%, with a better distribution of BMI values in the metropolitan area where there is the highest occurrence of positive conditions and behaviours: availability of sports facilities, the highest prevalence of sports practice, and the lowest prevalence of completely sedentary children.