Introduction: The prevalence of childhood and adolescent obesity is increasing, with negative medical and psychosocial consequences. Aims: This study examines the association between weight status and nutrient intake, sport and leisure habits of middle school students in Bologna (Italy). Methods: Anthropometric data (height, weight) of 598 subjects (321 males and 277 females) 11-14 years old were collected. Questionnaires on nutrient intake, sport and leisure behaviour were administered. Results: Protein, carbohydrate and total fat intakes of the adolescents were higher than the recommended ranges in all age groups and in both sexes. The proportion of energy from protein and total fat was higher than recommended, but the percentage from carbohydrate was lower. A significant proportion of the adolescents had a cholesterol intake above the Italian RDA and lower than recommended intakes for micronutrients. The prevalence of overweight and obesity is higher in males than in females at all ages (overweight: 35.2 vs 31.6 at 11 yrs.; 27.5 vs 20.2 at 12 yrs.; 18.6 vs 17.8 at 13 yrs.; 18.7 vs 10.9 at 14 yrs.; obesity: 5.5 vs 3.2 at 12 yrs.; 3.9 vs 1.1 at 13 yrs.; 5.3 vs 3.6 at 14 yrs.), except in subjects 11 years old (obesity: 7.4 vs 10.5). The overweight and obese adolescents consumed less carbohydrates and less fibre than their normal weight and underweight counterparts. Conclusion: The results of the present study indicate an unbalanced diet of the Bologna adolescents, which could damage their health and quality of life.