PURPOSE: Childhood obesity is an increasing public health issue worldwide. We examined dietary patterns among adolescents in a dormitory school, identified obese adolescents and tried to intervene to improve food habits and physical activity. METHODS: We conducted an experimental prospective longitudinal study based on 36 obese (body mass index [BMI]> or =95th percentile) adolescents (aged 12-18 years) compared with controls (healthy children: normal age-appropriate BMI (BMI< or =85th percentile). Six months' intervention included lifestyle-modification counseling (once a week by a clinical dietician), and an exercise regimen twice a week, 60 minutes each time, instructed by a professional pediatric trainer). Both groups underwent baseline measurements at the beginning of the study and 6 months later (arterial stiffness, blood pressure, pulse, weight and height, hemoglobin, creatinine, liver enzymes, highly sensitive C-reactive protein and complete lipid profile). RESULTS: Twenty-one participants completed the study. Low compliance from participants, school staff and parents was observed (participation in planned meetings; 71%-83%). BMI significantly decreased from 32.46+/-3.93 kg/m2 to 30.32+/-3.4 kg/m2 (P=0.002) in the study group. Arterial stiffness was not significantly different between the 2 groups and did not change significantly after 6 months' intervention (P=0.494). No significant changes in CRP and lipid profile were observed after the intervention. CONCLUSION: Making lifestyle modifications among adolescents in a dormitory school is a complex task. Active intervention indeed ameliorates BMI parameters. However, in order to maximize the beneficial effects, a multidisciplinary well-trained team is needed, with emphasis on integrating parents and the school environment.