This paper presents results from the first 4 years (2009 through 2012) of the B4School Check programme, a free health and development check for 4-year-olds that is part of the Well Child Tamariki Ora schedule of services. Demographic and body mass index (BMI) data were extracted for all children. Overweight and obesity rates were estimated using International Obesity Task Force (IOTF) 2012 standards and the 85th (overweight) and 95th (obese)percentiles for BMI-for-age of the World Health Organisation (WHO) 2006, Centers for Disease Control and Prevention 2000 and UK 1990 reference standards. The analysis included 168,744 BMI measurements, with a coverage rate of 66.5%. Mean BMI was 16.30 kg/m2 in girls and 16.44 kg/m2 in boys. Mean BMI z-score (WHO 2006 standards) was 0.601 in girls and 0.785 in boys. Prevalence of overweight and obesity varied between different reference standards. Using WHO 2006 standards, 16.9% of girls and 19.6% of boys were overweight and 13.8% of girls and 18.7% of boys were obese. Using IOTF standards, 18.3% of girls and 16.2% of boys were overweight and 5.7% of girls and 4.7% of boys were obese. Prevalence of overweight and obesity was higher in Pacific and Māori children and those living in more socioeconomically deprived areas than other children. No definite time-trends were observed over the study duration.
