OBJECTIVE: To compare lifestyle and health aspects among obese, overweight, and normal-weight 15-year-old boys living in the county of Västmanland, Sweden. DESIGN: A cross-sectional school-based survey. Setting. All schools in the county of Västmanland, Sweden. SUBJECTS: A questionnaire was completed anonymously by 989 boys. MAIN OUTCOME MEASURES: The relations between body mass index and social factors, eating habits, physical activity, body image, relations, school situation, use of alcohol, drugs and tobacco, somatic and psychological symptoms in boys. RESULTS: Obese boys had a significant negative outcome in 19 out of 31 items studied compared with normal-weight boys, while the overweight boys had a significant negative outcome in 9 out of 31. The obese boys reported more irregular eating habits than normal-weight boys, were less satisfied with their weight and looks, and had fewer friends. A larger proportion of the obese boys reported that they did not like school, were more absent from school, and had been exposed to more violence. They bullied their schoolmates more often. The obese boys had tried sniffing solvents and used illicit drugs more frequently than their peers. They reported more somatic and psychological symptoms as well as suicidal thoughts and attempts. CONCLUSIONS: Obese 15-year-old boys differed from overweight and normal-weight boys in lifestyle and in the frequency of somatic and psychological symptoms. Early and vigorous intervention is necessary, as they may belong to a risk group that could develop not only medically but also socially negative consequences.