computer assisted biopsy of breast tumors in this paper we report our preliminary results of the development of a computer assisted system for breast biopsy the system is based on tracked ultrasound images of the breast a three dimensional ultrasound volume is constructed from a set of tracked bscan images acquired with a calibrated probe the system has been designed to assist a radiologist during breast biopsy and also as a training system for radiology residents a semiautomatic classification algorithm was implemented to assist the user with the annotation of the tumor on an ultrasound volume we report the development of the system prototype tested on a physical phantom of a breast with a tumor made of polivinil alcohol