A flexible shaft (28) to be inserted into a channel of a living body provided with a plurality of adjacently abutting cells (26), the walls (30) of which are formed from wall sections. For this reason the flexible shaft (28), which is particularly cost-effective to produce and which demonstrates high flexibility paired with ample stability, is constructed such that in at least one cell (26) in the cross-section of the wall (30) a concave wall section (44, 46, 48) is circumferentially alternated with a corresponding neighboring convex wall section (50, 52, 54).