The aim of this study was to estimate the prevalence of child overweight in a regional sample of primary school-aged children, and to examine the relationships among child overweight, psychopathology, and social functioning. A cross-sectional survey was conducted in 2004 in 100 primary schools of a large French region, with 2,341 children aged 6–11 randomly selected. Child weight and height, lifestyle variables (leisure-time physical activity (LTPA), watching television (TV), playing video games), and socioeconomic characteristics were collected in parent-administered questionnaires. Child psychopathology outcomes were assessed using child- and parent-reported instruments (Dominic Interactive (DI) and Strengths and Difficulties Questionnaire (SDQ)). Overweight and obesity were estimated according to the International Obesity Task Force (IOTF) definition. Response rates to the parent questionnaire and DI were 57.4 and 95.1%, respectively. Final sample size was 1,030 children. According to the IOTF, 17.3% of the children were overweight, of whom 3.3% were obese. In univariate analysis, correlates of overweight were low parental education, low monthly income, Disadvantaged School Areas (DSAs), self-reported generalized anxiety, parent-reported conduct disorders, emotional problems, and peer difficulties. High monthly income was less frequently associated with overweight. In multivariate analysis, parent-reported peer difficulties (odds ratio (OR) = 2.06; 95% confidence interval = 1.27–3.35) and DSAs (1.88; 1.03–3.44) were independent factors significantly associated with child overweight. There was a trend of being overweight with elevated TV times (P for trend = 0.02). The psychosocial burden of excess weight appears to be significant even in young children. Findings should be considered for preventing strategies and public health interventions. School-based overweight prevention programs should be implemented first in disadvantaged areas together with information about weight stigmatization and discrimination.