OBJECTIVE: To identify the social and environmental determinants most strongly associated with overweight and obesity in Brazilian schoolchildren from a developing region. METHODS: Data were collected from a community-based survey of schoolchildren from the Valley of Jequitinhonha, Minas Gerais, Brazil. The sample was composed of 5 100 school children aged 6-18 years. Overweight and obesity were defined by body mass index based on the current method recommended by the World Health Organization in 2007. Social and environmental determinants were collected by using a structured questionnaire. RESULTS: The prevalence of overweight and obesity was 11.1% and 2.7% in girls and 8.2% and 1.5% in boys, respectively. The chance of overweight was higher in schoolchildren who engaged in remunerated work (odds ratio [OR] = 2.19, 95% confidence interval [CI] 1.30- 3.26), whose parents had higher education levels (OR = 1.52, 95% CI 1.12-2.07), who had two or fewer siblings (OR = 1.74, 95% CI 1.21-2.49), and who were in a high economic class (OR = 1.93, 95% CI 1.32-2.85). Schoolchildren who traveled by car to school (OR = 1.50, 95% CI 1.14-1.91), lived < 5 km from school (OR = 1.64, 95% CI 1.06-2.39), and consumed foods sold in the school cafeteria (OR = 1.56, 95% CI 1.19-2.16) presented high odds of being overweight. CONCLUSIONS: The background from a particular region of a country should be considered when implementing preventive measures regarding overweight and obesity, especially for very poor, developing regions like the Valley of Jequitinhonha. Measures taken should consider a multilevel intervention that includes the family, school, and physical environment.