Recent US systems allow the real-time acquisition of volume data, either by freehand 3D techniques or novel transducer hardware. However, the acquisition of large volumes is limited by the field of view of the US transducer and anatomical scanning windows into the patient. Mosaicing of several 3D US scans has been proposed to generate large US volumes. Still, US imaging specific characteristics and artifacts make it challenging to create high quality mosaics. For many clinical cases, especially interventions, additional high quality CT data is available. In this paper we present a novel multi-variate, multi-modal 3D US registration and mosaicing approach, which reduces the effects of ultrasound imaging artifacts on mosaic quality, by incorporating information from co-registered CT.