In this paper we present a technique for tracking borescope tip pose in real-time. While borescopes are used regularly to inspect machinery for wear or damage, knowing the exact location of a borescope is difficult due to its flexibility. We present a technique for incremental borescope pose determination consisting of off-line feature extraction and on-line pose determination. The off-line feature extraction precomputes from a CAD model of the object the features visible in a selected set of views. These cover the region over which the borescope should travel. The on-line pose determination starts from a current pose estimate, determines the visible model features, and projects them into a two-dimensional image coordinate system. It then matches each to the current borescope video image (without explicitly extracting features from this image), and uses the differences between the predicted and matched feature positions in a least squares technique to iteratively refine the pose estimate. Our approach supports the mixed use of both matched feature positions and errors along the gradient within the pose determination. It handles radial lens distortions inherent in borescopes and executes at video frame rates regardless of CAD model size. The complete algorithm provides a continual indication of borescope tip pose.