OBJECTIVE: To identify those perinatal parameters and characteristics predisposing children to an increased risk of overweight during infancy and preschool years. DESIGN: The analyses were performed using data from the Growth, Exercise and Nutrition Epidemiological Study In preSchoolers. SUBJECTS: A representative sample of 2374 Greek preschoolers 1-5 years old. MEASUREMENTS: Anthropometric data, such as body weight, recumbent length and standing height, were obtained by using standard procedures and measuring equipment. Structured interviews were conducted with both parents to collect information on anthropometric, demographic, medical and behavioral data. Finally, children's anthropometric data at birth, 6 and 12 months of age were recorded from their birth certificates and medical records. RESULTS: Children born large for gestational age were 4.59 and 2.19 times more likely for being overweight at 6 and 12 months of age, respectively, than children born appropriate for gestational age. On the other hand, children that were exclusively breastfed were 0.49 and 0.54 times less likely for being overweight at 6 and 12 months of age, respectively, than children that were exclusively formula fed. Furthermore, 3- to 5-year-old children born to mothers who were both active and passive smokers during pregnancy were 1.79 times more likely of being overweight compared to children born to nonsmoking mothers. Finally, having an overweight father significantly increased the likelihood of childhood overweight at 12 months, 1-3 and 3-5 years of age. CONCLUSION: Our findings showed that some of the perinatal parameters and characteristics examined in the current study predict overweight at infancy, while others at preschool years. Priority should be given to size at birth, breastfeeding, maternal smoking during pregnancy and parental overweight, when developing public health strategies to reduce the prevalence of childhood overweight and related chronic disease later in life.