The assessment of lung cancer involves off-line threedimensional (3D) computed-tomography (CT) image assessment followed by live bronchoscopy. While standard bronchoscopy provides live video of information inside the lung airways, it does not give any information outside the airways. This results in a low procedure success rate. The success rate can be improved if the physician receives 3D CT-based image guidance. We describe a fast robust method that provides 3D CT-based image guidance during live bronchoscopy. The method enables a continuous registration between the 3D CT image space and the real bronchoscopic video. At a top level, it involves an interleaving of continuous video tracking and CT-video fine registration. During video tracking, the bronchoscope?s 3D motion is estimated using a point-based 3D-2D pose estimation method. Registration is performed via a warpingbased Gauss-Newton method that uses a normalized crosscorrelation- based cost for measuring similarity between the bronchoscopic video and CT image data. The method operates at a real-time rate of 10 frames per second, which is over an order of magnitude faster than past approaches. This real-time performance enables live guidance during a procedure. The method is incorporated into a computerbased system for image-guided bronchoscopy and has been applied to human lung-cancer patients. Results are presented for a phantom and lung-cancer patients. Keywords: 3D medical imaging, video tracking, image registration, virtual endoscopy, image-guided surgery