The augmentation index (AIx) is a measure of systemic arterial stiffness, and previous studies have demonstrated an association between AIx and risk factors of cardiovascular disease (CVD). However, there is limited knowledge about the age and gender differences of the observed associations. Therefore, the aim of the present study is to examine the association's consistency at different ages and to see if the associations are the same in men and women. This study is based on 3432 subjects from The Copenhagen City Heart Study, a prospective epidemiological survey of a representative population in Denmark. All subjects had AIx measured non-invasively by the SphygmoCor device (SphygmoCor, West Ryde, Australia). To analyse the association between AIx and CVD risk factors multiple linear regression analyses were used stratified by gender and age. The main determinants of AIx were age, heart rate, height and systolic blood pressure in both age groups with few gender differences. Associations between AIx and cardiovascular risk factors further differed by age: In young subjects AIx was associated with cholesterol, high-sensitive C-reactive protein, current smoking, low weight, poor education and physical inactivity, whereas in subjects above age 60 AIx was associated with weight and current smoking in men. We found a modest association between AIx and traditional CVD risk factors and the association attenuated in subjects >60 years. Further longitudinal studies are needed to determine whether AIx is primarily a marker of CVD in younger subjects.Journal of Human Hypertension advance online publication, 9 June 2011; doi:10.1038/jhh.2011.59.