Introduction:
Childhood obesity is a major public health issue. The prevalence of childhood overweight and obesity has increased substantially in the last decades worldwide, affecting one in two children in some countries of Southern Europe. In 2010, the prevalence of obesity in children 7 or 9 years old in Greece was the highest in Europe.

Objectives:
Our aim was to investigate the changes in overweight and obesity among Greek primary school children who participated in Rounds 2 (2009-10), 3 (2012-13), 4 (2015-16) and 5(2019-2020) of the WHO Childhood Obesity Surveillance Initiative (COSI).

Methodology:
All COSI Rounds were performed in a nationally representative sample of Greek schools, in children aged 7.0-7.9 and 9.0-9.9. Questionnaires regarding student data, school environment and family environment were completed. Anthropometric measurements (body weight, height, waist and hip circumference) were taken by experienced dietitians. All answers and measurements were stored in a custom-built, secure web-based patient information system.

Results:
Overweight and obesity prevalence for both boys and girls in both age groups decreased both from 2010-2013 and from 2013-2016 From 2016 to 2019 no major differences were observed. Statistically significant decreases were observed for all groups from 2010-2016. The decrease was higher for girls compared to boys and for children age 9 compared to children age 7.

Conclusion:
The latest COSI results show that, while still very high, the prevalence of childhood obesity in Greece decreased since 2010, mainly due to several preventive interventions targeting primary school children. However, multiple strategies that will involve family, community and school staff and make use of novel approaches such as Big Data Analytics and smart devices must be adopted, in collaboration with Greek Ministries, in order to ensure the downward trend in the obesity epidemic.