This article alleges that two letters attributed to the philosopher David Hume (1711–1776) were forged in the twentieth century. The letters were first published in 1972 and 1973 by Michael Morrisroe, an assistant professor of English in the University of Illinois, Chicago Circle, after which they became monuments of conventional scholarship on Hume's life and writings. Both letters are cited without qualification by scholars of Hume's thought in dozens of publications, including Ernest Campbell Mossner's celebrated Life of David Hume (1980), and John Robertson's entry for Hume in the Oxford Dictionary of National Biography (2004). This article reconstructs the history and transmission of Hume's extant letters and attempts to account for why the forgeries published by Morrisroe were accepted as genuine. It makes a systematic case against the authenticity of the letters, and focuses in particular on the question of whether Hume met the Jansenist homme de lettres Noël-Antoine Pluche (1688–1761) and had access to his library, in Reims, in 1734. The article concludes with a discussion of the implications of the exposé for modern editorial scholarship and intellectual history.