Objective: To assess the nutritional status, food intake and physical activity patterns in schoolchildren attending 5th and 6th grade in basic schools from different socio-economic levels in the metropolitan region of Santiago. Design: Cross-sectional study in children 5th and 6th grade of eighteen basic schools in the metropolitan region of Santiago. Setting: Boys and girls aged 9-12 years from basic schools were evaluated in terms of physical capacity. An anthropometric evaluation was also performed which included weight, height and triceps and subscapular skinfold thicknesses. Food intake was evaluated by a 24 h recall, socio-economic level by the ESOMAR method and physical activity by a questionnaire. Subjects: Boys and girls aged 9-12 years (n 1732). Results: The average prevalence of overweight and obesity was 40 %, with the highest prevalence in males and those from lower socio-economic level. A majority (64 %) of the children had a low level of physical activity. A higher intake of fat and protein and a higher intake of carbohydrate were found in the higher and lower socio-economic levels, respectively. Both males and females showed adequacy greater than 75 % in macronutrient intake except for fibre, with both groups showing a deficit in the consumption of fruits, vegetables, legumes, fish and milk products according to Chilean recommendations. Conclusions: A high prevalence of malnutrition by excess was observed in both sexes and a better eating and physical activity pattern was seen in children from higher socio-economic level.