In order to provide estimates of overweight and obesity among Greek schoolchildren, and the adherence rates to the Mediterranean diet (MD), a nationwide survey was performed among fifth and sixth grade students aged 10-12 years old.A stratified sampling in 10 regions of the country was applied to voluntarily enroll a representative sample of 4786 children. Children were weighed and measured and completed a semi-quantitative food frequency questionnaire with a supplementary section for the assessment of dietary aspects and physical activity levels. Additionally, the KIDMED index was used to evaluate the degree of adherence to the MD.According to the IOTF cut-offs, overweight (OW) and obesity (OB) prevalence among boys was 29.9% and 12.9%, while in girls 29.2% and 10.6%, respectively. Only 4.3% of the children had an optimal KIDMED score. KIDMED score did not differ between boys and girls and no differences were detected between normal weight and OW and OB children. However, children from semi-urban or rural regions had higher score. Furthermore, children with higher KIDMED score reported following a healthier diet and having higher physical activity levels.The prevalence of childhood obesity in Greece is the highest ever reported together with low adherence rates to the dietary patterns of the MD. Current findings suggest an increased risk for even higher rates of obesity in adolescence and adulthood in the near future. Taking into account that children are also abandoning the traditional cardio-protective MD, the increased risk for future adverse health consequences seems evident.