AIM: To describe overweight and obese adolescents and to determine any correlations between an adolescent's body mass index (BMI) with personal (age, gender), lifestyle (sedentary/sport activities, smoking status) and parental (smoking status, BMI, number of cars) characteristics. METHODS: Cross-sectional data on weight, height and various characteristics from 2008 Greek adolescents (12- to 17-year olds, 50.85% boys), measured in 2005-2007, were used. RESULTS: Almost 1 in 5 (19.2%) boys and 1 in 7 (13.2%) girls 12-17 years of age were overweight while 4.4% of the boys and 1.7% of the girls were obese. The adolescents' age, mother's smoking status, father's and mother's BMI predicted boys' and girls' BMI (b = 0.551, 0.203, 0.110, 0.495 for boys, b = 0.233, 0.187, 0.180, 0.531 for girls, respectively, p < or = 0.05). Univariate analysis revealed that television watching/using personal computer/playing video games and playtime were not correlated with BMI, while an inverse association of exercising for > or = 5 h/week and BMI was found in both boys and girls (b =-1.098, -0.528, p = 0.005, 0.004 respectively). CONCLUSION: The results of our study underline the high prevalence of obesity during adolescence in Greece. Age and parental unhealthy behaviour (increased BMI and maternal smoking status) were positive predictors of increased BMI of adolescents in both genders.