This article proposes a reconstruction of the Sextan critique against the Pythagorean conception of number as principle of all existing things. Taking into consideration all the parallel passages concerning the presentation and the polemic about the Pythagorean doctrine, the present article proposes a division of the sceptical critique into two sections, the first one presenting the Pythagorean reasons to consider the numbers as principle existing apart from numbered things, and the second one presenting the arguments that Sextus himself built against (...) them. This paper will show that this structure is consistent with the sceptical method, which consists in pointing out the ἰσοσθένεια among different positions which leads to suspension of judgment. Regarding the Pythagorean doctrine that emerges from these passages, the present article discusses the way in which Sextus testified a juxtaposition between Pythagorean and Platonic doctrines, probably due to a Middle-Platonic or Neopythagorean elaboration, against which Sextus used Platonic concepts, adopting in original way arguments taken from the Parmenides and the Phaedo. Despite the ἐποχή about the nature of the number, this article will argue that Sextus did not avoid to use the number in practical daily life, in a way that is consistent with the sceptical practical criterion. (shrink)