Abstract: A guiding device for sub-cutaneous implantation of a veinous puncture needle, comprising a sheath provided with a bore extending according to a main axis enabling the needle to be introduced parallel to said axis, and flexible fins extending radially from said sheath, said fins having a lower surface which can be applied against the skin of a patient and which can assume a rest position wherein the lower surface extends along a plane which is substantially perpendicular to the main axis.