We present the system design and the methods of video-based guidance to assist with brain tumor biopsy procedures. The system comprises of a three-dimensional (3-D) position sensor, a CCD camera, a liquid crystal display (LCD) and a graphics computer equipped with a video capture board. The markers for positional measurement are attached to the CCD camera, a surgical tool, and the patient head. In order to be integrated into the camera-viewing capacity, 3-D images of the head and guidance indicators are visualized to form a life like video image. For reliable guidance, we also use the surgical plan, called the "safety map", which is a sphere surface highlighting the covering area of anatomically significant tissues and obstacles around the target for the indication of the biopsy needle's insertion starting-point. The safety map can be visualized in exactly the same way as it would be in a real life situation. The preliminary experiments were performed at the National Cancer Center. A high degree of flexibility in terms of views was created by using general apparatuses which are a CCD camera and a LCD. The display of the safety map enabled a successful completion of both craniotomy and biopsy needle insertion procedures.