Aim: To identify risk factors for overweight and obesity in Portuguese children. Methods: A cross-sectional study of children 7 to 9.5 y old was performed between October 2002 and June 2003. A total of 2274 girls and 2237 boys were observed. Weight and height were measured, and parents filled out a questionnaire about family characteristics. Overweight and obesity, using age- and sex-specific body mass index (BMI) cut-off points as defined by the International Obesity Taskforce, were used. Results: After adjustment for age and sex, the odds ratio for childhood obesity increased by television viewing (reference 0-2 h; 2-3 h: 1.51; 3-4 h: 1.72; ≥4 h: 1.63), paternal obesity (reference <18.5 kg/m²; 25.0-29.9: 3.06; ≥30.0: 7.09), maternal obesity (reference <18.5 kg/m²; 25.0-29.9: 9.06; ≥30.0: 18.13) and birthweight (reference <2500 g; 2500-3000 g: 1.55; 3000-3500 g: 1.87; 3500-4000 g: 2.13; ≥4000 g: 2.74), and decreased by sleeping duration (reference 8 h/d; 9-10 h/d: 0.44; ≥11 h/d: 0.39), paternal education (reference primary school; secondary: 0.91; university: 0.42), maternal education (reference primary school; secondary: 1.13; university: 0.56), being a single child (reference yes; no: 0.56) and family size (reference one child; two children: 0.59; three children: 0.44; more than four children: 0.37).

Conclusion: Our data support the perspective that education about energy intake and energy expenditure should be used much earlier in those families with high-risk children, namely those with high parental BMI or high birthweight. Protective factors were parental education and family size.