Additive manufacturing technology has made significant advances in terms of materials, tolerances, and surface finishes. The technique is becoming more common in science and industry. Since it has proven effective in constructing small parts with fine features, 3D printing is well suited for improving upon the manufacturing processes of millimeter-wave components. This paper explores the approach specifically applied to waveguide components produced using two different additive manufacturing approaches. One is a metal 3D printing process called Direct Metal Laser Sintering (DMLS). The other is high resolution stereolithography with metallic plating. Several millimeter-wave corrugated horns were “printed” in an aluminum alloy (AlSi10Mg) using DMLS, as well using Nickel-plated stereolithography. The testing of the components' electrical performance in terms of losses and radiation patterns at 100 GHz and 170 GHz is promising. Work is also being done to fabricate parts via additive manufacturing techniques in-house at General Atomics.