So far it has never been clearly decided whether the treatise De natura rerum constitutes an authentic work by the physician and natural philosopher Theophrastus Bombast of Hohenheim, called Paracelsus (1493/94–1541) This article outlines the manuscript and printing traditions of De natura rerum, in which a recently discovered manuscript from 1571 is identified as the earliest source. The watermarks of this manuscript refer to the Tyrolean Inn Valley, where great alchemical expertise was available due to silver mining. A detailed examination of the content and style of the preface and the nine chapters indicates the involvement of at least three different authors. Some of these parts are definitely forgeries, while others cannot be judged with certainty as to their authenticity. On the other hand, three chapters, those on death, resuscitation and the signature of natural things, are most likely real writings of Paracelsus.