Childhood obesity has become a modern epidemic with escalating rates. The aim of our study was the assessment of the association between extracurricular sports participation with the obesity status among Greek schoolchildren aged 10-12 years.Seven-hundred children (323 boys) aged 10-12 years were evaluated through a standardized questionnaire. Several lifestyle, dietary and physical activity attributes were recorded. Children according to the median hours of participation in after-school structured physical activity were classified as participating for more or less than 3 hours per week. Body height and mass were measured and body mass index was calculated in order to classify children as overweight or obese according to IOTF classification. Multiple logistic regression analysis was used in order to evaluate the association between the participation of more than 3 hours per week in structured physical activity after school with overweight or obesity.A total of 48.9% of the boys and 31.8% of the girls were participating for more than 3 hours per week (P<0.001) in extracurricular sport activities. Moreover, 33.9 % of the boys and 22.1 % of the girls were classified as overweight and 9.4% of the boys and 8.6% of the girls as obese (P=0.006). Girls who participated in excess of 3 hours in extracurricular sport activities were 59% less likely to be overweight or obese than their non participating counterparts, adjusted for several confounders (adjusted OR: 0.41, 95% CI: 0.20-0.83).Participation in extracurricular sports activity is inversely related to overweight or obesity in 10-12 years old Greek girls.