Fluoroscopic procedures are generally acknowledged to lead to large patient doses. It is important to have a method of measuring detector performance. Applications of cascaded‐systems theory to measure detector performance of fluoroscopic systems have produced unexpectedly high results due to the reduction in measured noise caused by temporal averaging between frames as a result of system lag. Methods have been proposed to remove this affect of lag, which require the system temporal resolution through the system temporal modulation transfer function (MTF). No method currently exists to easily and accurately measure the system temporal MTF of a fluoroscopic system. We have developed a novel technique, the “moving slanted‐edge method”, to make measurements of system temporal MTF from the image data of a fluoroscopic system. We translate a tungsten sheet across the detector with constant velocity, vo, and calculate a spatiotemporal coordinate for each pixel based on distance and time from passage of the edge. The resulting data is used to calculate a vo‐dependent MTF. The system (spatial) MTF and vo‐dependent MTF are mapped onto the temporal axis using the edge velocity. The system temporal MTF is calculated by dividing the vo‐dependent MTF by the (spatial) MTF. This method was validated on a bench‐top fluoroscopic system consisting of a three‐year old Dunlee image intensifier coupled to a CCD camera. The system temporal MTF was calculated using the moving slanted‐edge method (vo=45 cm/s) and the optical decay curve of the image intensifier. Excellent agreement was found between the two methods.