A system for aiding in the positioning of a medical instrument on the head of a patient, characterized in that it includes a means for predicting the location of a target intracranial area of the medical instrument, comprising a generic three-dimensional model of a head comprising a scalp and a generic target intracranial area, a three-dimensional working image of the scalp of the head of the patient, surface registration means suitable for establishing a registration transform from the scalp of the generic model toward the working image of the scalp of the head of the patient, a means for resampling the generic target intracranial area into a converted target area using with the registration transform, and a means for locating the target intracranial area of the patient from the locating of the converted target area, thereby enabling the positioning of the medical instrument on the head of the patient.
