In light of alarming rises in the prevalence of obesity worldwide, tackling the obesity 'epidemic' is now a national health priority in many countries. Increasingly, population measures that provide accurate estimates of body fatness are required to assist public health organisations in identifying at-risk groups and developing appropriate preventative strategies. Body mass index (BMI) remains the most cost-effective and practical tool in this regard. The World Health Organization (WHO) has issued universal BMI standards for defining 'overweight' and 'obesity' in adults (BMI > or =25 kg x m(-2), and > or =30 kg x m(-2), respectively) based on the risk of obesity-related disease in Europeans. Although widely used, there is mounting evidence suggesting that these standards are not appropriate for all populations. Research indicates that the associations between BMI, percent body fat (%BF), and health risks can vary across different ethnicities. Accordingly, ethnic-specific and country-specific BMI cut-offs for overweight and obesity may be necessary to attain valid prevalence estimates. In New Zealand, this area is largely unexplored in both young people and Asian populations. There is a need for large-scale longitudinal studies investigating the relationships between excessive body fatness and related health outcomes across all major ethnic groups in New Zealand.