A World Health Organization (WHO) Expert Consultation on Waist Circumference (WC) and Waist-Hip Ratio (WHR) was convened in Geneva from 8 to 11 December 2008 to consider approaches to developing international guidelines for indices and action levels in order to characterize health risks associated with these measures of body fat distribution-alternative or complementary to the existing WHO guidelines for assessments of generalized obesity on the basis of body mass index. Six background papers prepared for the Consultation are compiled in this issue. These six papers examine a range of health outcomes and issues, including whether there is a basis for choosing WC over WHR and whether different action levels by gender, age, ethnicity, country or region are warranted. Although guidelines involving WC and WHR are potentially useful and clearly required, the challenges in identifying cutoffs for international guidelines should not be underestimated or oversimplified. The final report and outcomes of the Expert Consultation will be published by WHO.