Sedentary lifestyles and energy-rich diets are driving an increasing prevalence of abdominal obesity, which is associated with cardiovascular risk. Reliable estimates of the worldwide prevalence of abdominal obesity are needed to quantify the associated health risk. The International Day for the Evaluation of Abdominal obesity (IDEA) study is a large, international epidemiological cross-sectional study designed to provide reliable data on the distribution of waist circumference according to region, gender, age, and socio-economic level in 177 345 primary care patients from 63 countries across five continents. Any non-pregnant patient aged 18–80 consulting one of the randomly selected primary care physicians on two pre-defined half days was eligible to participate in the study. The primary objective was to estimate the prevalence of abdominal obesity in primary care, in each participating country. Secondary objectives were to estimate the prevalence of hypertension, type 2 diabetes, dyslipidaemia, and smoking, and to evaluate their associations with abdominal obesity, according to age, gender, and socio-economic level and region. The IDEA study will provide the first global map of the prevalence of abdominal obesity and associated comorbidities in primary care practice.