Defining healthy weight," is not easy and for an adolescent with all concerns about newly developing physiognomy it is even harder. The aim of this study was to find out the frequency of obesity and the association between the body mass index (BMI), weight-control behaviors and self-perceived body weight status in high school students of a southern city of Turkey. The students from 10 schools were randomly selected among 46,271 students of 72 high schools in Adana from 1999 to 2000. The response rate was 94.8% (2,35212480). The Turkish version of Youth Risk Behavior Survey Questionnaire (YRBSQ) was completed by the students. The students' weights and heights were measured. The mean age was 16.5 +/- 1.0 years of age (range=14-21 years). The mean BMI was 21.0 +/- 3.1, 25.5% of students were underweight, 65.7% were normal, 6.4% were overweight and 2.3% were obese (p=0.0001). Of all students, 24.3% defined themselves as thin, 45.3% as normal, 24.9% as overweight and 5.5% as obese (p=0.0001). The percentage of girls defining their body weight as overweight and obese was significantly higher than the boys (p=0.0001). Of all students, 35.5% wanted to lose weight, 22.3% wanted to gain weight, 27.8% wanted to keep their current weight. Intention (p=0.0001) and interventions to lose weight such as going on a diet (p=0.0001), provocative vomiting (p=0.0001) and 24-hours starving (p=0.0001) were significantly higher in girls than boys. Of students, 26.8% (n=620) were on a diet program either to lose or to keep their body weight. There was significant relationship between being on a diet program and intention to change body weight (p=0.047). We concluded that adolescents living in Adana have relatively higher risk of being underweight than being obese and have unhealthy weight changing plans due to their misperception of their body images. Adolescents may be unconscious on plans and attempts to change their body weights and nutrition and we suggest that education on nutrition and health is required for adolescents.