A guide device (1) for inserting a surgical instrument inside a body cavity comprises a guide body (3), a stabilisation opening (11) and a stabilizing element (12) which can be slidingly engaged inside of the guide body (3) to come out from the latter through the stabilisation opening (11). In particular, the guide body (3) comprises a deformable portion (35) suitable to pass from a concave configuration, bending towards the inside to house at least partially therein the stabilizing element (12), to a convex configuration, bending towards the outside of the guide body (3) restoring the cross-section of the inner lumen (13a), and vice versa. The guide body is therefore able to shrink in diameter during the passage inside an introducer catheter and to reacquire the nominal diameter at the operative level.
