Abstract: This invention relates to a mammography apparatus and more particularly to the means for compressing a pressure plate of the apparatus against the breast. The mounting of the pressure plate is such that the pressure can be applied uniformly throughout the breast area. To enable such uniform pressure to be obtained, the pressure plate is connected at its opposite ends to slide means which slide on tracks mounted on the cone of the X-ray machine. For the determination of the thickness of the compressed breast tissue between the pressure plate and the film upon which the breast rests, a measuring rod is secured to the tracks and a pointer is attached to the means which move on the tracks.