The doctrine of idols is one of the most famous aspects of Bacon's thought. Yet his claim that the idols lead to madness has gone almost entirely unnoticed. This paper argues that Bacon's theory of idols underlies his diagnosis of the contemporary condition as one of ‘universal madness’. In contrast to interpretations that locate his doctrine of error and recovery within the biblical narrative of the Fall, the present analysis focuses on the material and cultural sources of the mind's tendency towards error. It explains the idols in terms of Bacon's materialist psychology and his exposé of the debilitating effects of language and traditional learning. In so doing, it highlights the truly radical nature of the idols. For Bacon, the first step towards sanity was to alert people to the prevailing madness. The doctrine of idols was intended as a wake-up call, preparing the way for a remedy in the form of his new method of inquiry. The paper concludes by indicating how Bacon's method aimed to treat ‘universal madness’, and it suggests that his diagnosis influenced John Locke.