The aim of the text is to investigate ways to provide an answer to the question ‘what is the disease of ageing’? This question is raised because of biogerontology’s endeavor of treating ageing. But also raised by many social scientific critiques of biogerontology. As will be demonstrated, much of this critique is directed to the ways that the ‘pathologization’ of ageing might affect the status of the elderly. My argument, however, is that to better understand what biogerontology’s ‘disease of ageing’ is, one needs to detach ageing from old age. In the end, two tentative answers to the question of the title are drafted.