This article challenges the generally accepted thesis that the emergence and dominance of chronic illness over the last half century is due to the receding tide of acute infectious diseases and an ageing population. Instead, through an analysis of contemporary reports in the Journal of the American Medical Association, it is argued that the construct of chronic illness emerged as part of a new focus on the downstream consequences of disease and as a means of transferring what had been seen as the natural processes of ageing and senescence into an explanatory model based on pathological processes. The widely accepted idea of an epidemiological transition in illness prevalence has served to conceal the ways in which medicine has extended its remit and suppressed alternative explanatory frameworks.