A method is provided for characterizing a mask having a structure, comprising the steps of: illuminating said mask under at least one illumination angle with monochromatic illuminating radiation, so as to produce a diffraction pattern of said structure that includes at least two maxima of adjacent diffraction orders, capturing said diffraction pattern, determining the intensities of the maxima of the adjacent diffraction orders, and determining an intensity quotient of the intensities. A mask inspection microscope for characterizing a mask in conjunction with the performance of the inventive method is also provided.