Objectives. To assess early growth characteristics and socioeconomic factors of children in relation to body mass index (BMI) and presence of overweight among four-year-old children. Methods. Two Child Health Centres (CHC) participated in the study. They were selected to obtain two populations of children featuring divergent socio-economic characteristics. Growth data registered at the CHCs from birth to the 4-year check-up were recovered. Overweight was defined by the BMI cut-offs established by IOTF. BMI values expressed as BMI standard deviation score (BMISDS) were used for analysis. Results. At the 4-year check-up, the BMISDS and the proportion of children with overweight (including the obese) were significantly higher in the district with lower socio-economic status. High BMI at birth and low socio-economic status of the population in the CHC-district were shown to be independent determinants for overweight and BMISDS at four years of age. Conclusions. More research is needed to understand the mechanisms and how intervention programs should be designed in order to prevent the development of overweight and obesity in children.