As is commonly known, the Mühimme Defteri is one of the historical sources most widely used by Ottoman history researchers. In the Islamic world, the Ottoman Empire in particular has a great variety of historical documents. Among them, the Mühimme Defteri is considered an extremely important source for the richness and the diversity of its content and for its continuity. The Mühimme Defteri is an indispensable source as the number of historical documents handed down in the Ottoman Period before the Tanzimat Era are limited. Therefore, a multitude of research has been carried out based on the Mühimme Defteri. The greater part of the Mühimme Defteri used in past research is archived in the Basbakanlik Osmanli Arsivi (BOA) in Istanbul. From the summer of 2002 to the spring of 2006, the author intensively reviewed all 73 Mühimme Defterleri fonds considered the oldest, those which date from the late 16^th century, as well as all other registers of the period categorized as Mühimme Defteri.<br>As the contents of the individual registers classified as Mühimme Defteri by the BOA have not been adequately investigated, for this paper, the author focused on explaining the contents of the historical documents by identifying those which really do not belong in the Mühimme Defteri. As discussed in previous research, fonds from the so-called Mühimme Defterleri, Mühimme Zeyli Defterleri, and A. DVN. MHM. Defterleri were categorized as Mühimme Defteri although they consist of many registers not recognized as general Mühimme Defteri. Thus among the materials that are classified as being part of the Mühimme Defteri in the BOA holdings, it is made clear which registers do not actually belong in the Mühimme Defteri and what kind of content those historical materials have.