A three-dimensional ultrasound (3D-US) system suitable for laparoscopic surgery that uses a novel magneto-optic hybrid tracker configuration. Our aim is to integrate 3D-US into a laparoscopic AR system. A 5D miniature magnetic tracker is combined with a 6D optical tracker outside the body to perform 6D tracking of a flexible US probe tip in the abdominal cavity. 6D tracking parameters at the tip are obtained by combining the 5D parameters at the tip inside the body, the 6D parameters at the US probe handle outside the body, and the restriction of the tip motion relative to the handle. The system was evaluated in comparison with a conventional 3D ultrasound system. Although the accuracy of the proposed system was somewhat inferior to that of the conventional one, both the accuracy and sweet spot area were found to be acceptable for clinical use.