Three recent developments hint at a paradigm shift in thinking about dementia: first, the importance of vascular risk factors has increased as these have been shown to be associated with all dementias; second, it is increasingly recognized that there is an heterogeneity in cognitive ageing, and third there is an emerging << life-course >> view of dementia that suggests that risk factors all along life time matter for cognitive outcomes. In this paper we discuss the application of this shift in thinking in relation to the results from the Whitehall II study; the specificity of this cohort is that it examines cognitive ageing trajectories starting in midlife. We discuss results relating to age, socioeconomic factors and vascular risk factors.