The invention relates to a method of determining the position of a catheter introduced along a guide wire inserted into a body, in which method an image of the guide wire and the body region at the area of the guide wire is acquired by means of an imaging method, the distance traveled by the catheter on the guide wire is measured and the position of the catheter in the body is determined on the basis of the measured distance. The invention also relates to a device for determining the position of a catheter introduced along a guide wire inserted into a body, which device includes sensor means for measuring the distance traveled by the catheter on the guide wire and means for determining the position of the catheter on the basis of the measured distance.