Contrary to what has been maintained by critics, this article argues that the apocryphal book by Avellaneda may have played a major role in Cervantes's Don Quixote. Cervantes's invective against his ¿enemy¿ Avellaneda turns out to be not only superfluous but also contradictory. Moreover, both René Girard's Mensonge romantique et vérité romanesque and especially Michel Foucault's Les mots et les choses are correct in diagnosing Don Quixote's sickness as a literary one. Therefore, it is not surprising that his cure should also be a literary one. In fact Avellaneda's book plays a decisive role in it. This article points out how the change in the symptoms of Don Quixote's sickness that occur from the turning point of Chapter LIX, where Avellaneda's book is specifically mentioned for the first time, and his eventual return to sanity, are linked to the intrusion of Avellaneda's Quixote into the Cervantine novel.