Objective: To determine trends in the prevalence of overweight and obesity in children in The Hague (the Netherlands) from 1999 through 2007. Design: Population-based study of a series of cross-sectional assessments of height and weight from electronic health records. Setting: Child Health Care (Municipal Health Service), The Hague. Participants: 50 961 children aged 3–16 years, with Dutch (59%), Turkish (17%), Moroccan (13%) or Surinamese South Asian (11%) ethnicity, representative of the four major ethnic groups in The Hague, with 85 234 weight and height measurements recorded in 1999–2007. Main outcome measures: (Trends in) the prevalence of overweight (excluding obesity) and obesity as defined by the International Obesity Taskforce cut-off points, using logistic regression with year as independent variable. Results: From 1999 through 2007 there was a decrease in the prevalence of overweight in Dutch girls from 12.6% to 10.9% (OR 0.96; 95% CI 0.95 to 0.98) and an increase in Turkish boys from 14.6% to 21.4% (OR 1.08; 95% CI 1.04 to 1.11). Obesity prevalence rose significantly in Turkish boys from 7.9% to 13.1% (OR 1.04; 95% CI 1.01 to 1.06) and in Turkish girls from 8.0% to 10.7% (OR 1.04; 95% CI 1.01 to 1.08). Dutch boys, and Moroccan and Surinamese South Asian boys and girls showed no significant trends. Conclusions: The declining prevalence of overweight in Dutch girls may indicate reversal of previous trends in the Netherlands. However, in Turkish children overweight prevalence and obesity is high and increasing. Further public health action is necessary, especially for Turkish children.