BACKGROUND/OBJECTIVE: To record the prevalence of overweight and obesity in primary-school children in relation to perinatal risk factors, parental body mass index and sociodemographics. SUBJECTS/METHODS: A sample of 2294 schoolchildren aged 9-13 years was examined in municipalities from four Greek counties. Weight and height were measured using standard procedures, whereas international thresholds were used for the definition of overweight and obesity. Perinatal and parental data were also recorded via standardized questionnaires. RESULTS: The prevalence of overweight and obesity was 30.5% and 11.6%, respectively, with a higher prevalence of obesity in boys compared with girls (13.7% vs 9.5%, P<0.02). Maternal smoking at pregnancy (odds ratio (OR) 1.37; 95% confidence interval (CI) 1.05-1.98), rapid infant weight gain (OR 1.69; 95% CI 1.20-2.38), paternal and maternal obesity (OR 2.25; 95% CI 1.45-3.48 and OR 2.14; 95% CI 1.28-3.60) were found to significantly increase the odds of children's obesity (apart from overweight), whereas Greek nationality (OR 1.06; 95% CI 1.01-1.39) was found to significantly increase only the odds of children's overweight. Maternal pre-pregnancy obesity (OR 2.15; 95% CI 1.27-3.70) and introduction of solid foods at weaning later than 5 months of life (OR 1.60; 95% CI 1.02-2.51) were also found to increase the likelihood of childhood obesity. On the contrary, children having older fathers (OR 0.55; 95% CI 0.37-0.80) or more educated mothers (OR 0.57; 95% CI 0.36-0.90) were less likely to be obese. CONCLUSIONS: The current study identified certain perinatal factors (that is, maternal pre-pregnancy obesity, maternal smoking at pregnancy, rapid infant weight gain and late introduction of solid foods at weaning) and parental characteristics (that is, younger fathers, Greek nationality, less educated and overweight parents) as important risk factors for children's overweight and obesity, indicating the multifactorial nature of their etiology and the need to extend our understanding beyond positive energy equilibrium.