A filtering lens for conical horns based on Metamaterials is presented. The paper focuses on a millimeter wave application. The metamaterial structure is composed of a printed layer of Split Ring Resonators (SRRs) on a substrate. The structure is used as a superstrate on the horn aperture. When the SRRs are excited, afilter performance arises preventing radiation in the desired frequency bands. Besides the filtering property, also a lens behavior is achieved. In this way larger gain can be achieved in both E and H planes, reducing the -3 dB beamwidth. A 6% -3 dB stop band is achieved from 73.3 GHz to 85.7 GHz. Symmetrisation of the radiation pattern up to 3 dB is accomplished and the focalization e®ect is achieved by emulating a hyperbolical-plane lens. Thus, a simplified system based on a conical horn can be designed by unifying the filter and lens in one electromagnetic element.