Prevention of early childhood obesity requires a clear understanding of its determinants. This study examined perinatal, parental, and lifestyle determinants of childhood obesity and how these factors are associated with maternal misperceptions of their children's weight status. The current work presents a cross-sectional analysis of 2,374 children, age 1 to 5 years, living in Greece (April 2003 to July 2004). The 2000 Centers for Disease Control and Prevention growth charts were used to classify children as overweight (≥85th and <95th body mass index [BMI]-for-age percentile for children older than 24 months) and obese (≥95th weight-for-length percentile for children younger than 24 months and ≥95th BMI-for-age percentile for children older than 24 months). Maternal perceptions about their children's weight status were assessed via interviews with the mothers. Early infancy growth data were obtained from pediatric medical records. The present study showed that the prevalence of overweight and obesity was 16.2% and 17.5%, respectively. Each unit increase of maternal and paternal BMI significantly increased the likelihood of childhood obesity by a factor of 1.03 (95% confidence interval [CI]: 1.01 to 1.07) and 1.15 (95% CI: 1.10 to 1.20), respectively. Furthermore, children with a rapid weight gain in infancy were 1.9 (95% CI: 1.3 to 2.7) times more likely to be overweight and 1.5 (95% CI: 1.2 to 1.9) times more likely to have their weight status underestimated by their mother. In conclusion, rapid infancy weight gain and higher parental BMI were the main determinants of obesity in preschool years. Maternal underestimation of children's weight status was more likely for children with rapid weight gain in infancy.