A method for determining, by means of a computer, a photolithography mask for the manufacturing a microstructure by grey level etching of a resist layer, this mask including a plurality of elementary cells, each including an opaque area arranged, in top view, in a non-peripheral portion of a transparent region or, conversely, in a transparent area arranged, in top view, in a non-peripheral portion of an opaque region, comprising the steps of: a) initializing the mask pattern in a first state; b) determining, by simulation, the profile of the microstructure which would result from the use of the mask according to said pattern; c) adjusting said pattern by modifying, in certain cells, the position of the opaque or transparent area within the cell; and d) forming the mask according to said pattern.