Abstract: A videofluoroscopy system for use in vivo, real-time, motion analysis includes a fluoroscopy system for producing a series of x-ray images of a subject, a video recorder for recording the x-ray images as video frame images, a video playback unit for providing a playback output of individual video image frames one at a time, a frame grabber connected to a display monitor for converting each image frame into graphics data and displaying a selected viewing area thereof on the monitor, a marking device for marking selected points within the viewing area of each image frame, and a computer processor for controlling the frame grabber, display, and marking device in order to define the viewing area, detect X-Y coordinates for the selected points, and store the coordinates of the marking points as motion data. The frame grabber is implemented as a module connected to the computer processor which automatically operates the video playback unit and converts the image frames one frame at a time to digital graphics data.