The aim of the present study, which was part of the Health Behavior in School Aged Children (HBSC) study, was to provide national estimates for overweight and obesity in Greek school-aged children and adolescents. A nationwide multistage procedure was followed to obtain a representative sample of children and adolescents aged 11.5, 13.5 and 15.5 y. The resultant sample consisted of 4299 students, 51.3% girls and 48.7% boys. Self-reported weight and height data were used. According to the body mass index cutoff points adopted by the International Obesity Task Force (IOTF), 9.1% of girls and 21.7% of boys were classified as overweight, and 1.2% of girls and 2.5% of boys as obese. Corresponding values using CDC growth charts were 8.1% of girls and 18.8% of boys for overweight, and 1.7% of girls and 5.8% of boys for obese. Compared to most other western countries, the prevalence of obesity is lower in Greek children aged 11–16 y.