A filter medium for cleaning fluids includes a filter layer (9) formed from a filter material in a pleated web with a longitudinal direction (X) and a transverse direction (Y). A plastic grid (10) forms a support layer, bears against the filter layer (9) and has linear elements (12, 14) delimiting through openings (16) between them. Two groups of linear elements (12, 14) extend approximately at right angles to one another and delimit rectangular through openings (16). The linear elements (14) having a smaller diameter (d2) are in direct contact with the filter layer (9). The linear elements (12) having a larger diameter (d1) and having a greater spacing from one another relative to the filter layer (9) rest on the smaller diameter linear elements (14).