The aim of the study was to determine socio-economic and parental factors affecting odds for development of obesity in school-age children from south-eastern Poland (SEP). 2,182 boys and 2,066 girls from randomly selected elementary schools in SEP were involved in this study. The mean age of the girls was 10.4 years (SD 2.4, range 6.7–14.9). The mean age of the boys was 10.5 years (SD 2.3, range 6.9–14.9). 167 boys (7.7%, 95% CI: 6.6–8.8%) and 208 girls (10.1%, 95% CI: 8.8–11.4%) were obese. The difference in prevalence of obesity between genders was statistically significant. Socioeconomic risk factors (RF) were different from those in Western Europe or the United States. A small number of siblings was RF for obesity. Intact family had a protective effect. No correlation was found between child’s obesity and parental education, income per capita or mother working outside the home. Parental obesity was RF for the obesity in children. High BMI at birth was an RF for obesity. A distinct pattern of socio-economic RF underlines the importance of population specific epidemiological studies. Defining RF in a specific region provides information to design specific preventive strategies.