We have developed a simple algorithm for scalp localization for craniotomy. Using a series of CT/MRI data, the point on the scalp closest to the center of the lesion (T) is determined by our program. A plane (plane R) is defined by three points: bilateral auditory meati and T. Point S is the intersection of three planes: the plane R, the scalp surface and the midsagittal plane. The distance from either S or the ipsilateral external auditory meatus to T is measured along the scalp surface on the plane R. The distance from the nasion to S along the scalp surface on the midsagittal plane is also measured. To determine the craniotomy site, these distances are measured directly on a patient’s scalp in the operating room. This simple and accurate method for scalp localization could be used by installing our program in conventional CT/MR scanners.