The invention relates to a filter medium for cleaning fluids, comprising at least one filter layer (9) which is formed from a filter material and which predetermines a preferably pleated web form of the filter medium having a longitudinal direction (X) and a transverse direction (Y), and at least one plastic grid (10) which as a support layer bears against at least one filter layer (9) and has linear elements (12, 14) which delimit through openings (16) between them. According to the invention said filter medium is characterised in that two groups of linear elements (12, 14) extend approximately at right angles to one another and delimit rectangular through openings (16), or that the linear elements (14) having a smaller diameter (d2) are in direct contact with the respective filter layer (9) of the filter medium and that the linear elements (12), which by contrast each have a larger diameter (d1) and have a greater spacing from one another relative to the associated filter layer (9) come to rest on the linear elements (14).