Leonardo Pisano’s Pratica Geometrie has been transmitted in thirteen handwritten witnesses, which have not yet been completely investigated. Three of them present a large text, which is not passed down in the other manuscripts: here Leonardo discusses and demonstrates the theorems 20 and 21 of the third book of Euclid’s Elements. The text has so far been ignored by the critics, even by the most recent, because its absence in the ms. Urb. Lat. 292 meant that the prince Boncompagni did not report it within his printed edition. Its "discovery" was made possible only thanks to the collation, that is currently on going, conducted on the known handwritten witnesses of the Pratica Geometrie.