The invention relates to a method for planning the introduction of a needle in a patient's body, wherein the needle (2) is coupled to a needle guide (3) tracked by a navigation system with respect to a 3D medical image (1) of the patient, comprising:- determining a virtual position and orientation of the needle (2) with respect to the 3D image (1) using navigation data of the needle guide (3);- detecting at least one inserted needle (2'; 2a', 2b', 2c') as a trace in the 3D medical image (1);- displaying a representation of the virtual needle (2) and a representation of a relative position of the virtual needle with respect to the at least one detected needle (2'; 2a', 2b', 2c').