The invention relates to a method for measuring structures on masks (1) for photolithography, wherein firstly the mask (1) is mounted on a spatially movable platform (2). The position of the platform (2) is controlled in this case. The structure on the mask (1) is illuminated with illumination light from an illumination light source which emits coherent light. The light coming from the mask (1) is imaged onto a detection device (6) by an imaging optical unit (4) and detected. The detected signals are evaluated in an evaluation device (7) and the positions and dimensions of the structures are determined. The invention also relates to an apparatus by which these method steps, in particular, can be carried out. In this case, the accuracy of the position and dimension determination is increased by the properties of the illumination light being coordinated with the structure to be measured. For this purpose, the illumination device (3, 3') has setting means for coordinating the properties of the illumination light with the structure to be measured.