Materials and methods: This cross-sectional study included a total of 1,357 adolescents between March 2011 and May 2012 in Beyoglu district of Istanbul province of Turkey. The questionnaire including 38 questions which was developed based on the Youth Risk Behavior Survey, which is used by the Center for Disease Control and Prevention (CDC), was used for the data collection. The weight and height of the participants were measured and their body mass index (BMI) values were calculated.

Results: Of all participants, 54.8% were females, 5% of them were underweight, 12.6% were overweight, and 2.6% were obese. Among the male participants, the BMI values were higher (21.06±3.32 kg/m2) than females (20.26±2.88 kg/m2) (p<0.0001). The obesity ratio was higher in males (p<0.0001) and in children of highly educated parents (p<0.05). Of the participants, 23.5% were physically active. Physical activity level was higher in males, compared to females (p<0.0001). The rate of breakfast habit was higher in males than females (p=0.002). Healthy diets and losing weight in a healthy way were more commonly accepted by the students in the public schools, compared to those in private schools (p<0.0001).

Conclusion: Obesity is an important public health problem and proper eating habits and regular physical activity should be encouraged. High-income families should also encourage their children to become more aware of the importance of physical activity. The right time for this is childhood and adolescence, in which permanent habits can be easily acquired. Keywords : Adolescent; diet; high school; obesity; physical activity